U.S.-led air strikes against al Qaeda-inspired militants in Syria pose a problem for moderate rebel opponents of Syrian President Bashar al-Assad.
The Western-backed rebels say they face a backlash from Syrians angered by the offensive, even though they have been kept in the dark about the air strikes against their enemies in Islamic State.
This could complicate Washington's plan to turn disparate rebel groups into a ground force to combat the militants.
The rebels say civilian casualties from the week-old air campaign and suspicion of U.S. motives are endangering the public support they have gained during their fight with Assad.
"There is popular anger towards us," said rebel commander Ahmed al-Seoud, who defected from the Syrian army in 2012 and leads a rebel group known as the 13th Division.
His group defines itself as part of the "Free Syrian Army" - loosely affiliated non-Islamist factions, some of which are backed by donors including the United States and Gulf Arab countries that have supported the uprising against Assad.
The 13th Division boasts 1,700 fighters and is in need of everything from boots to arms even though it has been a recipient of foreign aid. Its position as Western-backed means people see it as supporting the air strikes, said Seoud.
"We support air strikes, but air strikes against Islamic State and the regime," he said in an interview in the Turkish town of Reyhanli near the Syrian border.
The United States says it is investigating allegations of civilian deaths from the air strikes and takes great care to try to avoid them. Still, Syrians protested against the air strikes in several rebel-held parts of the country on Friday, footage posted on Youtube showed.
While Washington has said it will not cooperate with Assad, who it says has lost legitimacy as leader of Syria, its air strikes have steered well clear of any government targets.
That has further heartened Damascus, a year after the United States shied away from launching military action against Assad. In the week since they were launched, his forces have pressed their attacks on the array of groups ranged against them in three and a half years of civil war.
Syria's non-Islamist rebels are as keen as anyone to see the end of Islamic State, which has seized a third of the country, mostly by taking territory won from the government by other factions.
But they are also in a fight for survival against the Syrian army and its allies, including the Lebanese group Hezbollah.
Battling both Assad and Islamic State, poorly armed rebels have no interest in escalating their fight with the militants at this point unless they can be sure the Syrian air force will not attack them in whatever territory they capture.
Thus far, there has been no sign of coordination with the U.S.-led coalition that could provide such air cover, according to members of rebel groups that have been fighting both Assad and Islamic State in northern Syria.
"It is not to our advantage to fight (IS) at this time just because some Tomahawks are falling on them ... without knowing that the regime has completely lost air supremacy over us," said Abu Abdo Salabman from the political office of the Mujahideen Army, an FSA-affiliated group he said has 7,000 personnel.
"They will bomb us out and take any advances we have made," he said in an interview in the Turkish city of Gaziantep. "It will be like we're cooking the meal for the regime to eat in the end."
No sign of more weapons
The Mujahideen Army, formed at the start of the year from eight smaller rebel factions, is being vetted as a possible recipient of aid from donors including the US, Salabman said.
But he added that Washington "won't be able to mobilize friends on the ground without coming up with a complete plan for (Islamic State) and the regime".
A handful of FSA factions have received military training in an ostensibly covert training programme run by the CIA.
But Western states have been hesitant to provide significant military aid, fearing it could end up in the hands of extremists.
The United States is planning to train thousands of moderate rebels as part of its strategy to fight Islamic State. But the programme could take several years.
Rebels fighting in northern Syria say there has been no sign of an accelerated dispersal of weapons, though some said they were hopeful they would receive more soon.
The first night of air strikes included an attack on al Qaeda fighters affiliated with the Nusra Front in an area where FSA-affiliated groups also operate.
Some of the Western-backed rebels have condemned the air campaign as unwanted foreign intervention.
For some rebels, the approach taken by the United States has raised questions about its agenda: Washington informed Damascus ahead of the strikes, but not them, they say.
A U.S. defense official told Reuters there was not enough of a mature organization within the moderate Syrian opposition at this point to be talking about coordinating strikes with it.
As Islamic State positions are bombed further east, there has been no movement in a key front line near Aleppo, where FSA-affiliated groups including the Mujahideen Army are fighting to stop Islamic State advancing.
The same groups are also battling simultaneously on other fronts to stop government forces from encircling Aleppo.
Were the U.S.-led coalition to coordinate military action against Islamic State with rebels in Aleppo province, that would mark a big shift towards engaging them directly in the battle. But it has yet to happen, the rebels say.
"The contacts are still very weak, with respect to the air strikes. There was absolutely no coordination," said Hussam Almarie, a spokesman with FSA-affiliated groups in northern Syria. "They have promised us they will open the lines of coordination more."
The air strikes are part of what Obama has described as a strategy to degrade and destroy Islamic State, which has seized large areas of territory in both Syria and Iraq in a bid to reshape the Middle East.
The U.S. strategy includes training 5,000 Syrian rebels in the first year of a programme that Saudi Arabia has offered to host and could go on for several years.
General Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff, said on Friday a Western-backed opposition force of around 12,000 to 15,000 would be needed to retake areas of Syria controlled by Islamic State.
A limited amount of financial and military aid has been funnelled to moderate rebel groups in Syria via a body grouping states that have backed the uprising against Assad. The body, set up this year, marks a bid to better control the flow of aid.
One recipient is the Hazzm movement, which was formed at the start of the year from FSA factions. It has been supplied with American-made anti-tank missiles not previously seen in the war.
But it still suffers from a lack of weaponry that means it can only deploy a fraction of the 5,000 fighters to whom it pays a salary of $100 a month, said Abu Abdullah, a Hazzm commander.
"Hazzm is today seen viewed as backed by the USA, but the support it gets does not reflect this," he said.
The U.S. defence official said it was too early to be talking about broadly equipping new forces, since the U.S. program in Saudi Arabia is only now starting to get underway.
Support has turned into a double-edged sword as Hazzm tries to build support among Syrians in the areas where it is operating. Both the Mujahideen Army and Hazzm have issued statements condemning the U.S.-led coalition's air strikes.
"People say the coalition is with Bashar. This puts us - the moderate groups - in a difficult position vis a vis the Syrian people. They say: 'Your friends, the people who are supposed to be friends of Syria, didn't find a solution or even put in place a strategy to eliminate the regime of Bashar al-Assad'."
Abdullah said he did not blame the United States for not bombing Assad's forces, noting Russia would have vetoed any attempt to get legal backing for intervention in the United Nations Security Council.
"But you can't explain this to a child whose father has been killed," he said. "Or a woman who was raped in jail and has a child from an unknown father, or a mother who lost four or five children."