By Tom Perry, Suleiman Al-Khalidi and John Walcott

BEIRUT/AMMAN/WASHINGTON (Reuters) – CIA-coordinated military aid for rebels in northwest Syria has been frozen since they came under major Islamist attack last month, rebel sources said, raising doubts about foreign support key to their war against President Bashar al-Assad.

Rebel officials said that no official explanation had been given for the move this month following the jihadist assault, though several said they believed the main objective was to prevent arms and cash falling into Islamist militant hands. But they said they expected the aid freeze to be temporary.

The halt in assistance, which has included salaries, training, ammunition and in some cases guided anti-tank missiles, is a response to jihadist attacks and has nothing to do with U.S. President Donald Trump replacing Barack Obama in January, two U.S. officials familiar with the CIA-led program said.

The freeze reflects the troubles facing Free Syrian Army (FSA) rebels in the almost six-year-old revolt against Assad, who now appears militarily unassailable in his core western region largely thanks to direct intervention on his side by Russia and Iran.

“The reality is that you have changes in the area, and these changes inevitably have repercussions,” said an official with one of the affected FSA rebel groups. He said no military assistance could “enter at present until matters are organized. There is a new arrangement but nothing has crystallized yet”.

The support funneled to vetted FSA factions has included contributions from Turkey, Qatar and Saudi Arabia – states that have opposed Assad. It is one of several foreign aid channels to rebels. Others still function.

The CIA declined comment on the reported freeze in support. A Qatari official said his government had nothing to say on the matter. Turkish officials said only they could not discuss “operational details”. There was no word from Saudi Arabia.

Reuters confirmed the freeze with officials from five of the FSA groups that have been recipients of financial and military support from the so-called “MOM operations room”. It was also confirmed by two other senior FSA figures briefed on the matter.

They spoke on condition of anonymity given the covert nature of the CIA-backed program and the sensitivity of the subject.

Several rebels believed the aid halt was temporary, with new arrangements expected, but there was no clarity yet. Confirming the freeze, two senior FSA sources said donor states were aiming to send the aid to one, unified fighting force – a coherence that has eluded rebels throughout Syria’s civil war.

One of the FSA officials said he did not expect the rebels to be abandoned as they represent the best hope for blocking a further expansion of Sunni jihadist influence in Syria, and to fight back against the growing role of Iran there.

DECLINING REBEL FORTUNES

Idlib and nearby areas of Aleppo, Hama and Latakia provinces are among the last footholds of the anti-Assad insurgency in western Syria – the part of the country where he has shored up his rule by holding onto the main cities and the coast.

Islamists have long been seen as the more formidable insurgent force in the northwestern Idlib area though a dozen or more U.S.-vetted FSA groups have also operated there and nearby.

Last month’s militant assault on the FSA groups was launched by a group formerly known as the Nusra Front, al Qaeda’s official affiliate in the war until last year when it formally cut ties and renamed itself Jabhat Fateh al-Sham.

The jihadist onslaught led several FSA groups to merge with the powerful Islamist faction Ahrar al-Sham, widely believed to be backed by Assad’s foreign adversaries in the region.

That will likely give pause to foreign donors: Ahrar al-Sham is set apart from the FSA factions by a strongly Sunni Islamist ideology and it has previously fought alongside the Nusra Front.

Military aid to rebel groups has ebbed and flowed throughout the life of the program, U.S. officials said, as Washington and its allies have kept a close eye on any leakage to more militant factions, something one official called “a constant problem”.

TRUMP’S SYRIA POLICY NOT YET CLEAR

Before assuming office, Trump suggested he could end support for FSA groups and give priority to the fight against Islamic State (IS), whose well-armed jihadists hold large tracts of eastern and central Syria.

But Trump’s administration has yet to declare a firm policy towards Syria and Iraq, despite his repeated vows to eradicate IS, so it has been “business as usual” with covert and overt training and military support programs, one U.S. official said.

Some FSA groups hope Trump’s animosity towards Iran could yet result in enhanced U.S. support.

Jihadist forces attacked while FSA envoys attended Russian-backed Syria peace talks in Kazakhstan, accusing the rebels of conspiring with Moscow and Washington against Jabhat Fateh al-Sham. The United States has carried out a deadly series of air strikes against Fateh al-Sham in Idlib this year.

MOM-backed rebels had suffered a heavy blow in December when Syrian government forces ousted them from eastern Aleppo with decisive help from the Russian air force and Iranian-backed militias. Eastern Aleppo had been seen as an FSA stronghold.

An official with an FSA group that has received MOM aid said none came this month “and there are no signals”. Another said a regular meeting of the MOM had been canceled this month.

“I expect a reorganization,” he said, adding that there were still around 15,000 combatants with FSA groups in the northwest.

The CIA-backed program has regulated aid to the rebels after a period of unchecked support early in the war – especially from Gulf states – helped give rise to an array of insurgent groups, many of them strongly Islamist in ideology.

A similar program continues to operate in southern Syria with Jordanian backing. Some of the FSA groups backed through the MOM in the north continue to receive Turkish support as they participate in the Turkey-led Euphrates Shield offensive against IS and Kurdish groups to the northeast of Aleppo.

FSA groups have long complained that the aid provided falls far short of what they need to confront the better armed Syrian army. Their demands for anti-aircraft missiles have been consistently rebuffed.

U.S. intelligence and military officials said the leakage, sale and capture of U.S.-supplied and other weapons from units of the FSA to Islamic State, the Nusra Front, and other splinter militant groups have been a concern since the CIA and U.S. military began arming and training a limited number of rebels.

From the start, said one of the officials, some U.S.-backed rebels have migrated from groups that were battered by Syrian government forces to others such as IS that were seizing and holding territory at the time. Aid has slowed or stopped in Idlib and nearby areas, officials said, amid fears the pattern may be continuing after rebels lost ground there.

Another U.S. official said FSA groups continue to mount significant challenges to Assad. “Despite the setbacks and no assistance in fighting back against a brutal Russian onslaught, the fact is they remain a viable fighting force,” the official said.

(This story has been refiled to remove repetitive words in 4th paragraph)

(Additional reporting by William Maclean in Dubai, Nick Tattersall, Humeyra Pamuk and Orhan Coskun in Turkey, Jonathan Landay in Washington; writing by Tom Perry; editing by Mark Heinrich)