Just ahead of the fourteenth anniversary of al Qaeda's 9/11 attacks on the U.S., the leader of the terrorist group took aim in an angry speech at a mortal enemy -- but not American “crusaders” this time. Rather, the object of his tirade was the leader of ISIS in a declaration of war that will “irreconcilably” divide the two terror groups in a way the U.S. may be able to exploit, experts say.

Ayman al-Zawahiri, the Egyptian doctor who replaced Osama bin Laden as the head of al Qaeda four years ago, in a new audio message accused ISIS top leader Abu Bakr al-Baghdadi of “sedition” and insisted the Iraqi terrorist recluse was not the leader of all Muslims and militant jihad as “caliph” of the Islamic State, as al-Baghdadi had claimed 14 months ago in a Mosul mosque.

Had ISIS and al Qaeda realigned by joining forces, it “would be terrible,” said Olsen, an ABC News contributor.

That division -- now formally declared by the highest ranking official of the group that slaughtered almost 3,000 Americans 14 years ago in multi-pronged aviation attacks -- could provide an opening that American counter-terrorism operatives could find a way to exploit, he added.

Olsen said the U.S. could use misinformation to further pit the two jihadi menaces against each other and encourage the series of gunfights and assassinations each has waged against the other -- like when ISIS reportedly killed a top Zawahiri emissary trying to broker a ceasefire between the fighters in Syria in February 2014.

The fledgling franchise in Afghanistan and Pakistan, known as IS Khorasan Province, “has been fighting non-stop” with the Taliban and al Qaeda there, a counter-terrorism official told ABC News. “Fighting each other makes our job easier,” said the official in Afghanistan.

In the new audio tape, which was released online Wednesday and accompanied by a still image or al-Zawahiri and text of his speech, the al Qaeda leader appeared to confirm that he had not directly addressed infighting among the jihadis of ISIS and al Qaeda’s Syrian wing, Jabhat al-Nusra or the al Nusra Front, for fear of legitimizing ISIS.

ISIS, formerly the al Qaeda branch in Iraq, split from the larger group two years ago. In the tape, al-Zawahiri complained that Baghdadi had ignored Muslims suffering in Gaza and in Pakistan.

“We preferred to respond with as little as possible, out of our concern to extinguish the fire of sedition,” Zawahiri explained, “but Abu Bakr al-Baghdadi and his brothers did not leave us a choice, for they have demanded that all the mujahideen reject their confirmed pledges of allegiance, and to pledge allegiance to them for what they claim of a caliphate.”

“Everyone was surprised” by Baghdadi’s declaration anointing himself the fourth caliph in Islamic history, Zawahiri remarked, saying al-Baghdadi had done this “without consulting the Muslims.”

Al-Zawahiri's sour grapes speech, however, appeared to have been recorded last spring, analysts said, and reiterated past pledges of loyalty to Taliban leader Mullah Omar, who recently was confirmed dead by the Taliban. That appeared to mark a rare misstep for al Qaeda and al-Zawahiri, who once was able to leak his videotaped response to news events as quickly as one week later, but who now is in hiding with a $25 million U.S. bounty on his head.

Nicholas Palarino, a recently retired senior congressional counter-terrorism adviser who teaches about terrorism at Georgetown University, said al-Zawahiri being forced to call out al-Baghdadi weakens the power of both al Qaeda and ISIS and may offer Arab governments a window of opportunity to drive a wedge between the jihadi groups and those who are flocking to fight in Syria and Iraq.

“Moderate Muslims need to exploit this rift. The leaders of Jordan, Kuwait, Saudi Arabia and Egypt can explain the differences between these two groups to the world’s Muslims,” Palarino said.

Though it didn't foresee the rise of ISIS, former CIA Director Michael Hayden said the intelligence community had predicted a rift in al Qaeda emerging after bin Laden's death -- something like what's happening now between ISIS and al Qaeda, which the U.S. could use to its advantage.

"It would be a good idea to do so. We always thought that the death of bin Laden could create a rift between the Egyptians and the other Arabs inside al Qaeda since Zawahiri was an Egyptian. Seems to have played out," former CIA Director Michael Hayden told ABC News.

When it comes to exploiting the rift between two deadly extremist groups, however, Hayden cautioned, "You need to be careful."

BUDAPEST, Hungary (AP) — Soaked to the bone and ankle deep in mud, thousands of people seeking refuge in Europe are finding that their path to a new life is growing harder by the hour.

Torrential rains poured as an unprecedented 7,000 trekkers crossed the Greek border into Macedonia on Thursday past rows of camouflage-jacketed police. Children stumbled into mud-filled potholes and had to be pulled back out, bawling, into their mothers' arms. People struggled to find anything — plastic sheets, garbage bags, even a beach umbrella — to shield themselves from an unrelenting deluge.

And yet nothing could dampen their hopes of reaching the heart of Europe, where asylum and border security systems are already in danger of being overwhelmed in the migration crisis.

"I'm not going to be afraid of anything," said Waseem Absi, a 30-year-old from Ariha in northern Syria, as he held a disassembled pup tent over his head and trudged up a muddy slope alongside four friends. He said he hopes to reunite with relatives in the Netherlands.

The sudden onset of autumn has taken tens of thousands by surprise all along the Balkans route from Greece to Hungary, the main gateway to Western Europe for more than 160,000 asylum seekers already this year.

As recently as last week, those making the epic journey, much of it on foot, were baking in a region-wide heat wave and free to sleep under the stars. Now they're without shelter and struggling to keep campfires burning, highlighting the inadequate support provided by several European governments at each border crossing.

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A girl cries as refugees and migrants try to cross the borders in heavy rainfall from the northern G …

Conditions also rapidly deteriorated on Hungary's southern border with Serbia, where an estimated 3,000 crossed at an approved rail site or illegally by ducking under the razor-wire marking that frontier. Garbage-strewn fields turned to mud, trapping relief agency trucks whose wheels spun and flecked passing migrants with sodden earth.

With Hungary and other nations providing few facilities on their borders, travelers have poured into the few tents erected recently by relief workers trying to compensate for the lack of government support.

"The medical tent is full of people — people who aren't actually sick, by the way, but just want a warm place to sit down. We can't get rid of them," said Gabor Gyurko, a volunteer for the Catholic charity Caritas, which is providing medical care at a police-supervised collection point. Medics gave first aid to several mothers and their children and covered them with thermal blankets.

Gyurko said he expected the volume of ill people to surge with the chilly, wet weather "especially among people living in such close quarters."

International aid workers said Hungary has failed to provide sufficient shelter at migrant bottlenecks on the border, particularly near the village of Roszke. The country instead is investing in a new security regime, supposed to begin Sept. 15, designed to close its border with Serbia backed by more than 3,000 troops, many of whom conducted drills Thursday in cooperation with Serbian colleagues.

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A woman holds a girl as she passes the border from the northern Greek village of Idomeni to southern …

"The situation here is really a big disaster because a lot of refugees are coming every hour from the border from Serbia to Hungary, to Roszke, and we don't have real infrastructure here," said Kathrin Niedermoser, whose Austrian charity for asylum seekers provided what food it could keep from getting wet. "We have small tents, now it's raining, and all the things are getting wet."

She said Hungary should deploy "big tents where people can come, sleep and have a rest. We don't even have electricity, which means we don't have warm water during the whole day."

Conditions improved farther north on the route. Austrian police said more than 6,000 crossed Thursday from Hungary, chiefly near the town of Nickelsdorf, where authorities struggled to find enough buses, trains and emergency shelter. Most went to nearby towns, but more than 1,000 stayed in huge halls filled with beds near the border.

Earlier, Austria's rail company suddenly canceled all of its cross-border service with Hungary, citing what it called "a massive overload."

That raised tensions at Budapest's main Keleti station, where dozens of daily trains were scheduled to reach the Austrian capital, Vienna. Several hundred people from the Middle East, Asia and Africa waited up to 10 hours with tickets in hand as police penned them into one area. Volunteers from the Migration Aid charity used bullhorns to try to reassure the crowd in both Arabic and English that the trains would come.

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Macedonian border police helps refugees and migrants to pass in heavy rainfall from the northern Gre …

Confusion reigned as Keleti's huge arrivals and departures board showed many westbound trains to Austria, but two dozen police in surgical masks and gloves — a measure they take fearing the foreigners might have contagious diseases — blocked their access to the platforms. Hungarians and other international passengers were ferried by police along the edge of the asylum seekers to the trains.

As rumors spread that Austria was canceling services, officials scrambled to shift train schedules. After hours without clear information and amid tears of joy and relief, police gradually allowed the crowd through to trains to the border near Nickelsdorf, where they faced short walks to Austrian aid workers.

"My husband is waiting for me in Vienna. I cannot wait to see him," said Nuha al-Gumaa, a native of Aleppo, Syria, who was traveling with two brothers and her four children, including daughters Gaber, 3, and Nadine, 4. "We were on the border (with Serbia) a day ago, but reached here by walking and by bus. We slept in a garden last night. We all want so badly for this journey to be done."

The International Organization for Migration reported Thursday that 432,761 people have entered via Mediterranean routes, either from Libya to Italy or from Turkey to Greece, so far this year. That shattered previous forecasts that such traffic might reach 400,000 by the end of 2015.

Germany, the most popular destination for asylum seekers because of Chancellor Angela Merkel's pledge to provide refuge particularly to Syrians, has received more than 30,000 people since Saturday, when it and Austria struck an emergency deal with Hungary to accept thousands who had marched out of refugee camps and Keleti station toward Austria.

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But Austria said it was reviewing its policy of permitting Germany-bound migrants to pass through without even registering and expressed hope that Hungary's tougher border measures would allow the country to regain control of its own asylum system.

A growing immigration crisis (video)

Denmark initially sought to block hundreds of asylum seekers from trying to pass through the country to Sweden, another top destination because of its strong reputation for welcoming refugees.

But Denmark's police chief, Jens Henrik Hoejbjerg, said the country would permit all asylum seekers to reach Sweden unimpeded. That decision flies in the face of European Union rules that refugee claims should be made in the first EU entry point.

"We can't detain foreigners who do not want to seek asylum here," Hoejbjerg said. "There is no other option than to let them go, and we cannot prevent them from traveling wherever they want."

More than 3,200 had entered Denmark from Germany since Sunday, of which just 668 people have sought asylum, he said.

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Swedish Prime Minister Stefan Lofven expressed surprise that Denmark hadn't stopped the asylum seekers because "all countries must register refugees."

In the Syrian capital of Damascus, the government of President Bashar al-Assad made a rare comment on the migration crisis, saying Europeans only had themselves to blame for backing rebel groups fighting the government for the past four years.

Information Minister Omran al-Zoubi said people mostly were fleeing areas held by anti-government forces, including the Islamic State group. He said Europe "sent terrorists" to Syria and imposed economic sanctions designed to drive people from the country. Government-held territory remained safe, he said, and "any Syrian abroad can return to his country any time he wants."

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Associated Press writers Costas Kantouris in Idomeni, Greece, Alexander Kuli and Balint Szlanko in Roszke, Hungary, Philipp-Moritz Jenne in Nickelsdorf, Austria, Pablo Gorondi in Budapest, Jan Olsen in Copenhagen, Denmark, Jamey Keaten in Geneva, Switzerland, and Albert Aji in Damascus contributed to this report.

WASHINGTON (AP) — The U.S. Senate voted to uphold the hard-fought nuclear accord with Iran on Thursday, with Democrats overcoming ferocious Republican opposition and delivering President Barack Obama a legacy making victory on his top foreign policy priority.

A disapproval resolution for the agreement fell two votes short of the 60 needed to move forward as most Democratic and independent senators banded together against it. Although House Republicans continued to pursue eleventh-hour strategies to derail the international accord and Senate Republicans promised a re-vote, Thursday's outcome all but guaranteed that the disapproval legislation would not reach Obama's desk.

As a result the nuclear deal will move forward unchecked by Congress, an improbable win by Obama in the face of unanimous opposition from Republicans who control Congress, Republican candidates seeking to replace him in the Oval Office and the state of Israel and its allied lobbyists in the U.S.

Beginning next week, Obama will be free to start scaling back U.S. sanctions to implement the agreement negotiated by Iran, the U.S. and five other world powers. The accord aims to constrain Iran's nuclear ambitions in exchange for hundreds of billions of dollars in relief from international sanctions.

"This vote is a victory for diplomacy, for American national security and for the safety and security of the world," the president said in a statement. "Going forward, we will turn to the critical work of implementing and verifying this deal so that Iran cannot pursue a nuclear weapon."

Frustrated Republicans railed against Democrats for using a procedural vote to block final passage of the disapproval resolution, and issued grim warnings about a deal they contend could serve only to enrich Tehran and leave it closer to building a bomb when constraints begin to ease in 10 or 15 years. They promised that Thursday's vote would not be the Senate's last word, and moments after it was over Senate Republican Majority Leader Mitch McConnell set the stage for another next week.

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U.S. Secretary of State John Kerry (C) listens as U.S. President Barack Obama meets with a group of …

"No amount of saying this issue is over makes it over," McConnell declared, adding that if a Republican wins the White House next year, "I say to Iranian observers of the debate, (the deal) will be looked on anew."

But Democrats led by Minority Leader Harry Reid of Nevada promised that any further votes would have the same outcome "and are just simply a waste of time."

"People around the world should know today's outcome was clear, decisive and final," Reid said.

In the House, Republicans had not given up on blocking the deal against all odds. After backtracking on plans to vote on the disapproval resolution when it began to look short of support in the Senate, House Republicans lined up votes on several related measures.

Late Thursday they agreed on a party-line 245-186 vote to a measure specifying that Obama had not properly submitted all documents related to the accord for Congress' review, and therefore a 60-day review clock had not really started.

House Republicans revolt against Iran nuclear votePlay video

That will be followed Friday by votes on a bill to approve the accord — which is doomed to fail, but Republicans want to force Democrats to go on record in favor of the agreement — and on a measure preventing Obama from lifting congressionally mandated sanctions on Iran.

"This debate is far from over, and frankly, it's just beginning," said House Speaker John Boehner, a Republican. "This is a bad deal with decades-long consequences for the security of the American people and our allies. And we'll use every tool at our disposal to stop, slow, and delay this agreement."

Underscoring the fierce politics, the National Republican Senatorial Committee sent out press releases within moments of the Senate vote criticizing Democratic senators for their votes.

Some House Republicans, buoyed by a favorable ruling this week in a lawsuit they filed over Obama's health care law, have begun suggesting a lawsuit to stop the accord. Boehner called that "an option that is very possible."

Yet the House Republican maneuvers seemed to have little chance of bearing results, and White House officials sarcastically branded them the "Tortilla Coast Gambit," a reference to a Capitol Hill restaurant where tea party lawmakers plan their moves. Even before the Senate voted, White House Press Secretary Josh Earnest was boasting of the administration's success.

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Associated Press writers Darlene Superville, Nancy Benac, Alan Fram and Mary Clare Jalonick contributed to this report.