Tehran (AFP) - Iran's Foreign Minister Mohammad Javad Zarif on Monday dismissed as of "no legal value" a letter from 47 US senators warning that any nuclear deal will require Congressional approval.

In an open letter to the Islamic republic, the 47 Republicans, including Senate leaders and several potential 2016 presidential candidates, reminded Iranian leaders that President Barack Obama is in office only until January 2017, and a successor could scrap the agreement if Congress has not approved it.

"We believe that the letter has no legal value and is propaganda," Zarif said, quoted in Iranian media.

"The senators must know that under international law, Congress cannot change the content of the agreement.

"Any congressional action to prevent the implementation of any agreement will violate the international commitments of the (US) government.

"The world is not just in America," Zarif added.

The letter appeared to be another bid to influence or even derail the talks underway between Tehran and the P5+1 group of world powers to rein in Iran's contested nuclear programme.

It marked a rare foray by Congress into US foreign policymaking, as negotiating with foreign governments is a responsibility typically handled by the executive branch, not lawmakers.

Washington (AFP) - Barack Obama pilloried Republicans over an incendiary letter to Iran's leaders that warned a nuclear deal with the United States could be scrapped by the next president.

Forty-seven Senate Republicans -- including several potential 2016 presidential candidates -- made the unprecedented move of directly and publicly addressing leaders of the Islamic Republic in a bid to scupper the sensitive talks.

"It has come to our attention while observing your nuclear negotiations with our government that you may not fully understand our constitutional system," the letter said.

Republicans warned any deal agreed before Obama leaves office in 2017 is "nothing more than an executive agreement between President Barack Obama and (supreme leader) Ayatollah Khamenei."

"The next president could revoke such an executive agreement with the stroke of a pen and future Congresses could modify the terms of the agreement at any time," they added.

Obama reacted by saying he would make his case to voters.

"I think it is somewhat ironic to see some members of Congress wanting to make common cause with hardliners in Iran," Obama said. "It is an unusual coalition."

"What we are going to focus on right now is actually seeing whether we can get a deal," added Obama.

"Once we do, if we do, then we'll be able to make the case to the American people."

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Secretary of State John Kerry (2nd L) stands next to Iranian Foreign Minister Mohammad Javad Zarif ( …

- Biden slams 'dangerous' move -

Vice President Joe Biden, a former senator with decades of experience in Congress, opened fire with a harsher edge saying Republicans put the United States in peril with their misstep.

"The letter sent on March 9th by forty-seven Republican Senators to the Islamic Republic of Iran, expressly designed to undercut a sitting President in the midst of sensitive international negotiations, is beneath the dignity of an institution I revere.

"This letter, in the guise of a constitutional lesson, ignores two centuries of precedent and threatens to undermine the ability of any future American president, whether Democrat or Republican, to negotiate with other nations on behalf of the United States," he said.

"This letter sends a highly misleading signal to friend and foe alike that our commander-in-chief cannot deliver on America's commitments -- a message that is as false as it is dangerous.

"Honorable people can disagree over policy. But this is no way to make America safer or stronger," Biden added.

It is rare for bitter US partisan divides to bleed over to a party actively undermining foreign policy.

But with talks on a deal to curb Iran's nuclear program now in the final stages, the adage that "politics stops at the water's edge" has been tossed overboard.

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The initiator of the letter, freshman Senator Tom Cotton, seen here, said that while the final terms …

Republican leaders recently invited Israeli Prime Minister Benjamin Netanyahu to address a joint meeting of Congress, despite White House anger over the visit.

Netanyahu, just weeks before a re-election bid, warned a brokered deal would not prevent Iran from getting nuclear weapons.

Instead, he said, "it would all but guarantee that Iran gets those weapons, lots of them."

With a March deadline looming, negotiators are furiously working to agree on a deal that would curb Iran's nuclear program in return for reducing Western sanctions.

- 'Sand in the gears' -

A new round of talks between US Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif is due to take place in Lausanne, Switzerland on March 15.

The deal is seen as a key foreign policy goal of the Obama administration.

Many Republicans -- and several Democrats -- fear such an accord would loosen economic sanctions on Tehran while leaving it free to secretly attempt to develop nuclear weapons technology.

Iran insists it is developing nuclear power for civilian purposes.

A bipartisan group of lawmakers recently introduced legislation requiring Obama to submit any pending deal with Iran for congressional approval.

But Senate Majority Leader Mitch McConnell, who signed Friday's letter, agreed to delay consideration of the bill, amid complaints from Democrats.

The White House accused Republicans of partisanship, throwing "sand in the gears" and holding a false belief that military action could stall Iran's nuclear program.

Senate Democratic Leader Harry Reid spoke out against the Republican's "unprecedented" intervention in sensitive international negotiations "with the sole goal of embarrassing the president of the United States."

But the initiator of the letter, freshman Senator Tom Cotton, said that while the final terms have yet to be hammered out, details that have emerged already make the deal unpalatable.

"We know so far that Susan Rice, the president's national security advisor, has already conceded that Iran will have a robust uranium enrichment capability," Cotton told Fox News.

"The president has said this deal will have a sunset, perhaps as little as 10 years. Those two terms alone make this deal unacceptable -- dangerous to the United States and dangerous to the world."

A Chadian soldier poses for a picture at the front line during battle against insurgent group Boko Haram in Gambaru, February 26, 2015. REUTERS/Emmanuel Braun

By Abdoulaye Massalaki and Madjiasra Nako

NIAMEY/N'DJAMENA (Reuters) - About 15 soldiers from Chad and Niger died in fighting to take control of two towns in northern Nigeria from Boko Haram, the first gains against the militants in a joint offensive launched at the weekend, military sources said on Monday.

About 30 Nigerien and Chadian soldiers were wounded in the clashes over Malam Fatouri and Damasak, a day after thousands of troops crossed the border to seize areas held by the Sunni Islamist group, whose insurgency has forced Nigeria to delay an election and neighbors to mobilize their armies.

A Chadian officer, who asked not to be named, said about 10 Chadian soldiers were killed and 20 wounded in fighting for the towns. Two sources with Niger's military told Reuters five of its soldiers were killed in the clashes.

There was no official comment from the armies of either Chad or Niger.

"We have kicked the enemy out of these areas and they are now under our control," a Niger military officer said.

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Chadian soldiers walk in front of a building that Boko Haram insurgents used as their base before be …

The advancing troops had seized large quantities of arms and ammunition as well as vehicles, he said, and were undertaking a clean-up operation in the area. "The troops have taken dozens of Boko Haram elements prisoner," he added.

Damasak, the town furthest into Nigeria, is 10 km (6 miles) south of the Niger border, where Nigerien and Chadian troops had been massing in recent weeks before the offensive.

A medical source in Diffa, the capital of the Niger region which borders Boko Haram's heartland in northeastern Nigeria, said 30 wounded soldiers had been admitted to the town's hospital.

A second Niger military source said about 300 Boko Haram militants had been killed. There was no official confirmation of the toll and it was not possible to verify the figure.

"We had permission from Nigeria for this action," the source said.

There was no immediate comment from Nigeria, which has launched its own offensive against the militants. Their gains forced Nigeria to delay elections that were due in February.

Boko Haram's six-year insurgency, which aims to carve out a caliphate in Nigeria's northeast, has killed thousands. The group has pledged allegiance to Islamic State, which rules a self-declared caliphate in parts of Iraq and Syria, according to an audio clip posted online on Saturday.

Cameroon, Chad, Niger and Benin have mobilized forces this year to help Nigeria defeat the group after it seized large amounts of territory and staged cross-border attacks.

Nigeria and its neighbors have been working to pull together plans and rules of engagement for a regional force of 8,700 troops but cooperation between the region's armies has been strained at times.

(Reporting by Abdoulaye Massalaki; Writing by David Lewis and Joe Bavier; Editing by Giles Elgood and David Stamp)

Baghdad (AFP) - The Islamic State group has publicly beheaded three men in northern Iraq, two of them for allegedly engaging in homosexual acts, according to photos shared by sympathisers on social media Tuesday.

The jihadist group, which controls swathes of Iraq and neighbouring Syria, has carried out hundreds of executions as it has imposed its brutal version of Islamic law, many of them photographed or videotaped.

The latest images did not show the claimed beheadings and their authenticity could not be independently verified.

A series of photographs shows the blindfolded men kneeling in the centre of what appears to be a traffic circle with a crowd of people looking on as a masked, black-clad executioner stands by with a long, rusty blade.

Accompanying captions said the trio were then executed, the third of them for alleged blasphemy.

The photos were said to have been taken in Nineveh province -- the first to fall to a sweeping IS-led offensive last June -- but the exact location was not specified.

Iraqi troops and militia are battling to push the jihadists back with support from a US-led coalition and Iran.

But retaking Nineveh and its capital Mosul poses a major challenge for Baghdad's forces, as the militants have had more than nine months to dig in.

Iraqi forces launched a huge operation last week aimed at retaking the city of Tikrit that, if successful, would serve as a stepping stone towards Mosul.