CIA-trained Syrian rebels, who had started to make serious gains on President Bashar Assad’s forces, are now under Russian bombardment with little prospect of rescue by their American patrons, U.S. officials say.

Officials, who spoke to The Associated Press on condition of anonymity, say Russia has directed parts of its airstrikes against U.S.-backed groups and other moderate opposition in an effort to weaken them. The White House has few options to defend those it had secretly armed and trained.

Rep. Mike Pompeo, R-Kan., who serves on the House Intelligence Committee, told the Associated Press the Russians “know their targets, and they have a sophisticated capacity to understand the battlefield situation. They are bombing in locations that are not connected to the Islamic State group.”

The CIA began its covert operation in 2013 to arm, fund an train a moderate opposition to Assad. Over that time, the CIA had trained an estimated 10,000 rebel righters. The effort was separate to the militants that were trained to fight ISIS exclusively. That program was widely considered a failure, and on Friday, the Defense Department announced it was abandoning the goal of a U.S.-trained Syrian force, instead opting to equip established groups to fight the Islamic State.

The New York Times first reported Friday that the existing training program would be shuttered. The Times report said a small group of “enablers,” or leaders, indeed would be instructed at a small center in Turkey going forward, and taught to be able to call in airstrikes. But batches of rebels reportedly will no longer go through training in other camps.

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For years, the CIA effort had floundered, so much so that some in Congress proposed cutting its budget. Some CIA-supported rebels had been captured; others had defected to extremist groups. The secret program was the only way the U.S. is taking on Assad militarily. The U.S. has mainly focused its efforts on fighting ISIS and urging Assad to leave office under his own power.

"Probably 60 to 80 percent of the arms that America shoveled in have gone to Al Qaeda and its affiliates," said Joshua Landis, a Syria expert at the University of Oklahoma.

But in recent months, CIA-backed groups, fighting alongside more extremist factions, began to make progress in Syria's south and northwest, American officials say. In July and August, U.S.-supported rebels seized territory on the al-Ghab plain, in northwest Syria's Idlib and Hama governorates. The plain is a natural barrier between areas controlled by Sunni Muslims and the Alawite sect to which Assad and his loyalists belong. The capture of the al-Ghab plain was seen as a breakthrough toward weakening the Alawites.

Those and other gains put Damascus, the capital, at risk, officials say.

However, recently, Russian airstrikes have hit groups in that area, according to the Institute of the Study of War. Russian bombs and missiles have hit specific buildings associated with the moderate Syrian opposition, according to a U.S. official briefed on the intelligence.

Russian officials have repeatedly insisted they are bombing ISIS militants and other terrorists.

Gen. Lloyd Austin, head of U.S. Central Command, admitted last month that only "four or five" fighters from the program were actually on the battlefield.

And he acknowledged the U.S. would fall far short of its original goal of training 5,400 in the first year.

At that point, the Pentagon had spent $42 million (out of $500 million set aside for the training program) to vet, arm and pay dozens of rebels. Lawmakers have been visibly frustrated at the lack of progress.

At last month's Senate Senate Armed Services Committee hearing with Austin, Sen. Claire McCaskill, D-Mo., challenged the Pentagon's request for $600 million for more training next year.

"We're counting on our fingers and toes at this point," she said of the trained fighters.

Sen. Jeff Sessions, R-Ala., called it a "total failure."

Fox News' Jennifer Griffin and Lucas Tomlinson and The Associated Press contributed to this report.