ANKARA, Turkey (AP) — Turkey's prime minister vowed Sunday his country won't be drawn into Syria's civil war, despite twin car bombings the government believes were carried out by a group of Turks with close ties to pro-government groups in Syria.

The bombings left 46 people dead and marked the biggest incident of violence across the border since the start of Syria's bloody civil war, raising fears of Turkey being pulled deeper into a conflict that threatens to destabilize the region.

Syria has rejected allegations it was behind the attacks. But Turkish authorities said Sunday they had detained nine Turkish citizens with links to the Syrian intelligence agency in connection with the bombings in the border town of Reyhanli, a hub for Syrian refugees and rebels just across from Syria's Idlib province.

Harsh accusations have flown between Turkey and Syria, signaling a sharp escalation of already high tensions between the two former allies. But Prime Minister Recep Tayyip Erdogan suggested that Turkey would not be drawn militarily in retaliation.

He insisted Turkey would "maintain our extreme cool-headedness in the face of efforts and provocations to drag us into the bloody quagmire."

"Those who target Turkey will be held to account sooner or later," he said. "Great states retaliate more powerfully, but when the time is right... We are taking our steps in a coolheaded manner."

Turkish Foreign Minister Ahmet Davutoglu told reporters in Berlin those detained were linked to a Marxist terrorist group.

Sabah, a Turkish newspaper close to the government, reported Sunday that authorities suspect the leader of a former Marxist group, Mirhac Ural, now believed to be based in Syria, may have revived his group and ordered the attack.

The group, Acilciler, was one of many Marxist groups active in Turkey through the 1970s and 1980s, and was long-rumored to have been formed by the Syrian intelligence agency. Many of its militants allegedly included ethnic Arab Turks belonging to a sect close to Syria's Alawites.

"Some believe that now that relations (with Turkey) have deteriorated again, Syria may have reactivated the group to cause turmoil in Turkey," said Nihat Ali Ozcan, a terrorism expert at the Ankara-based Economic Policy Research Foundation of Turkey.

Guler said a ringleader was among those detained, and more arrests were expected.

"We have determined that some of them were involved in the planning, in the exploration and in the hiding of the vehicles," he said.

Saturday's twin bombings 15 minutes apart damaged some 735 businesses and 120 apartments, leaving smoking hulks of buildings and charred cars. It also wounded dozens of people, including 50 who remained hospitalized Sunday.

Syria and Turkey became adversaries early on during the uprising against Syrian President Bashar Assad that erupted in March 2011. Since then, Turkey has firmly sided with the Syrian opposition, hosting its leaders along with rebel commanders and providing refuge to hundreds of thousands of Syrian refugees.

Deputy Prime Minister Besir Atalay said the aim of the attack was to stoke tensions between Turks and Syrian refugees. The town is home to members of Turkey's Arab Alevi community, an offshoot of Shiite Islam, while many of the refugees who have fled Syria are Sunni.

On Sunday, hundreds of people marched in the city of Antakya, near Reyhanli, protesting the government for its Syria policies and support for the rebels — which some believe has exacerbated the conflict in Syria. Turks in Hatay, the southern province where the town is located, complain that the rebels roam freely, disrupting calm in Turkey's border regions.

Witnesses said they saw Turks attacking Syrian registered cars in Reyhanli soon after Saturday's attack and some Syrians avoided going out in the streets. Erdogan asked citizens in Reyhanli to remain calm and not "fall for the provocations."

"The prime minister brought this on to us," said a business owner, who asked to be identified only by his first name, Mehmet. "We have no peace anymore. The Syrians are coming in and out, and we don't know if they are bringing in explosives, taking out arms."

Authorities had so far identified 35 of the dead, three of them as Syrians. Families began burying their loved ones in funerals on Sunday.

Earlier in Damascus, Syrian Information Minister Omran al-Zoubi rejected Turkey's charges, saying that "Syria didn't and will never undertake such acts because our values don't allow us to do this."

He accused Turkey of destabilizing the border areas between the two countries by supporting the rebels, who the regime has labeled terrorists.

"They turned houses of civilian Turks, their farms, their property into a center and passageway for terrorist groups from all over the world," Al-Zoubi said. "They facilitated and still are the passage of weapons and explosives and money and murders to Syria."

Al-Zoubi also branded Erdogan a "killer and a butcher," adding that the Turkish leader "has no right to build his glory on the blood of the Turkish and Syrian people."

Tensions had earlier flared between the Syrian regime and Turkey after shells fired from Syria landed on the Turkish side, killing five Turks, and prompting Germany, the Netherlands and the U.S. to send two batteries of Patriot air defense missiles each to protect their NATO ally.

Davutoglu said his country would hold those responsible for the bombings but had no immediate plans to involve its NATO allies.

The attacks come just a little over a week after Israel escalated its role in the Syria conflict by striking suspected shipments of advanced Iranian weapons in Syria.

Erdogan is flying to the U.S. for talks with President Barack Obama next week. In the wake of the car bombs, both men could come under greater pressure to take action.

"It comes down to an existential struggle," said Salman Shaikh, director of the Brookings Doha center. "Those who oppose Assad really have to show that they mean it now."

The U.S. has provided humanitarian aid to the Syrian opposition, but has been reluctant to provide military aid, in part because al-Qaida-linked militants are becoming increasingly influential in the armed opposition.

Last week, Erdogan alleged that Syria has been using chemical weapons, delivering them on at least 200 missiles, though he provided no evidence. Syria has denied using chemical weapons.

Obama has portrayed the use of chemicals by the regime as a "red line" that would have harsh consequences, but has said he needs more time to investigate allegations.

In another potentially destabilizing element, Israel signaled last week that it will keep striking at shipments of advanced Iranian weapons that might be bound for Hezbollah. Syria has traditionally be a conduit for Iranian weapons to Hezbollah.

Earlier this month, Israel struck twice at what Israeli officials said were shipments of advanced Iranian missiles near Damascus. In response, Hezbollah chief Hassan Nasrallah said this week that Syria is expected to deliver "game-changing" weapons to his militia. If more than empty rhetoric, this would likely provoke more Israeli strikes.

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Associated Press writers Albert Aji in Damascus, Karin Laub and Zeina Karam in Beirut and Geir Moulson in Berlin contributed.

McCain (ABC News)

Sen. John McCain continued his criticism of the White House's handling of the Sept. 11 attacks in Benghazi, Libya, calling for a select committee to investigate what he called the Obama administration's "cover-up."

"Now, what you’ve got to look at this in the context of the times there," McCain told Martha Raddatz in an interview that aired on ABC's "This Week" on Sunday. "We are in the midst of a presidential campaign. The narrative by the Obama campaign is that bin Laden is dead, that al Qaeda is on the run, not to worry about anything, and her comes this attack on Benghazi. And there are so many questions that are unanswered. We need a select committee."

"The president didn’t call it an act of terror," the Arizona Republican continued. "In fact, two weeks later, before the U.N., he was talking about hateful videos and spontaneous demonstrations. What he did say the day after was he condemned acts of terrorism, but then that night ... and throughout the next two weeks, he kept saying that it was caused by a spontaneous demonstration sparked by a hateful video. He kept saying that over and over again and condemning that."

McCain repeated his assertion that the administration is guilty of a "cover-up."

"I’d call it a cover-up," he said. "I would call it a cover-up to the extent that there was willful removal of information, which was obvious."

[Related: McCain claims ‘massive cover-up’ on Benghazi]

Last week, fellow Republican Sen. James Inhofe suggested President Obama could be impeached for his role in the case.

"Of all the great cover-ups in history—we’re talking about the Pentagon Papers, the Iran-Contra, Watergate and all the rest of them—this is going to go down as the most serious, most egregious cover-up in American history," Inhofe said.

In the interview that aired Sunday, McCain did not invoke the "i-word."

"With all due respect, I think this is a serious issue," he said. "I will even give the president the benefit of the doubt on some of these things. [But] we need a select committee."

[Also read: White House rebuffs Boehner on Benghazi-related emails]

McCain said he'd like to see former Secretary of State Hillary Clinton—who testified before Congress on Benghazi before leaving her post—testify again. Emails, uncovered last week, suggested the White House's talking points on Benghazi underwent 12 revisions.

"She had to have been in the in the loop some way, but we don’t know for sure," McCain said. "What I do know is that her response before the Foreign Relations Committee—'Who cares?' Remember when she said, 'Well, who cares how this happened?' in a rather emotional way? A lot of people care, I say with respect to the secretary of state."

Clinton, though, is not McCain's only target.

"We need a select committee that interviews everybody," McCain said. "I don’t know what level of 'scandal' this rises to, but I know it rises to the level where it requires a full and complete ventilation of these facts. Now, here we are, nine months later, and we’re still uncovering information which frankly contradicts the original line that the administration took. And so, we need the select committee and I hope we’ll get it. And the American people deserve it."

The backlash over handling of consulate attack has turned into the first TV ad against a potential Hillary Clinton run in 2016.

Video: Benghazi investigation has Hillary Clinton under fire