ISTANBUL: The prospect of ending Syria’s conflict through negotiations grew even more unlikely Monday, as the U.S. said it would not stop others from arming the rebels and a main opposition group prepared to set up a rival government to President Bashar Assad’s regime.

U.S. Secretary of State John Kerry said the Obama administration still wanted to leave the door open for a political solution.

But concerning Syria’s rebels, “the United States does not stand in the way of other countries that made a decision to provide arms, whether it’s France or Britain or others,” Kerry said, speaking in Washington.

His comments came after French President Francois Hollande said last week that his country and Britain were pushing the European Union to lift its arms embargo on Syria as soon as possible so that they could send weapons to rebel fighters.

The two countries are seeking military help for the rebels by the end of May or earlier if possible.

Germany and other EU nations have been skeptical, pointing to the risk of further escalation.

Britain and France argue that Assad will not hold genuine negotiations if he believes he can survive militarily and that strengthening the rebels is the only way of squeezing the regime.

Kerry’s remarks indicate that the Obama administration will not interfere with any country seeking to rebalance the fight against Assad’s regime.

The United States has long argued that more weapons in Syria would only make peace harder. As the violence has worsened over the last year, Washington has tempered that message somewhat.

It is now promising nonlethal aid to the anti-Assad militias in the form of meals and medical kits, and refusing to rule out further escalation.

The chairman of the Joint Chiefs of Staff, Gen. Martin Dempsey, said he was advising the Obama administration to “proceed cautiously” on Syria, in part because the United States is increasingly unclear about the makeup of rebel forces.

“About six months ago we had a very, let’s call it opaque understanding of the opposition, and now I’d say it’s even more opaque,” he said in remarks at the Center for Strategic and International Studies.

In Istanbul, the opposition Syrian National Coalition met to elect a prime minister who would run an interim government in Syria’s rebel-held areas. The election is set for Tuesday.

Setting up such a government, in a direct challenge to the regime, could harden battle lines even more and close the door to negotiations between Assad and the opposition.

The U.S. has been cool to the idea of a rival government, saying the focus should be on a political transition. Under a plan endorsed by the international community last year, Assad’s supporters and opponents were to propose representatives for a transition government, with each side able to veto candidates.

However, the plan did not address Assad’s role. Most in the Syrian opposition rule out any negotiations with the Syrian ruler.

The Syrian National Coalition, largely based in exile, has wrestled for weeks with a decision on setting up an interim government. The exiles could have trouble asserting their authority in war-ravaged regions, and the risk of failure is high.

“Expectations will be high and means will be low,” said coalition member Louay Safi.

However, Safi believes support for an interim government will grow if it shows it can deliver services to people in the rebel-run territories. “Anyone who tries to oppose it will be in a difficult position,” he said.

All those attending the Istanbul conference said they opposed negotiations between the opposition and the Assad regime on the terms of ending the war.

“We’ve heard a lot about this ‘peaceful solution,’ but there are no positive, real steps from the regime, and the opposition presented its plan and it is clear that the regime was just playing for time,” said Nizar al-Hrakey, another coalition member.

The election of a prime minister is set to for today.

The coalition’s 73-member general assembly is choosing among 12 candidates for the job.

Earlier Monday, the head of the main rebel group, the Free Syrian Army, lent his support to the idea of an interim government.

Gen. Salim Idriss said fighters affiliated with the FSA would recognize the authority of such a government. “We consider it the only legal government in the country,” Idriss said in Istanbul.

He also portrayed the FSA as the most powerful and organized rebel formation in Syria.

But it remains unclear how many of the hundreds of rebel brigades fighting Assad’s forces follow Idriss’ commands or are linked to his group.

Some of the most effective rebel groups are Islamic extremists who have developed their own support networks.

One of them, the Nusra Front, has been designated a terrorist group by the United States and is said to be linked to Al-Qaeda.

Idriss said his group had no relationship with the Nusra Front.

He renewed his call for world powers to arm rebel fighters, saying his group would ensure the weapons did not fall into the wrong hands –a prime concern of the United States and other powers, especially given Syria’s southern frontier with Israel.“We have the power and the organizational capacity to control the movement of these weapons and keep them in safe, trusted hands,” he said.