The Pentagon said Tuesday that its program to train and equip moderate Syrian rebels to fight the Islamic State in Iraq and Syria has temporarily stopped receiving new recruits at its training sites.

"We continue to recruit and vet potential participants for the [train and equip] program. As we review the program, we have paused the actual movement of new recruits from Syria," Pentagon press secretary Peter Cook said.

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"We also continue to provide support for current forces on the ground and to train the cohorts currently in the program," he said.

CBS News first reported on Monday that the program was "put on hold" after some of the rebels handed over their U.S.-supplied equipment to al Qaeda's affiliate in Syria, al Nusra Front, but officials initially pushed back against the report.

It's unclear who made the decision to suspend taking in new recruits and when.

A U.S. Central Command spokesman on Tuesday morning said he was not aware of any suspensions. Another defense official said recruits were still training, but were unsure if there was a decision to stop training future recruits.

Asked whether the Pentagon had suspended the program, a Defense Department spokeswoman said the "program is active and is undergoing an internal review to determine what areas can be improved."

The White House also pushed back against suggestions that any part of the program was suspended.

"We have clearly faced challenges with the Train & Equip program, and we are currently reviewing our efforts to determine how we can do better," National Security Council spokeswoman Emily Horne said on Tuesday afternoon.

"We will continue our support for those forces on the ground while also continuing to refine and improve the Train & Equip program," she said. "While it would be premature to speculate about any changes to the program, we remain committed to the goals of our Train and Equip mission; that is, to enable forces on the ground to fight ISIL."

And Cook also vigorously pushed back against reports training had stopped.

"The training is on-going right now, and if something changes we will let you know," he said.

When asked directly if there was a pause in recruiting new people into the program, Cook said, "The program -- the training continues, and in terms of new recruits, I'm going to have to get back to exactly on the status of new recruits."

His later admission that the sending of new recruits for training to sites outside of Syria had paused comes after a series of bad news about the beleaguered program.

After having an initial goal of training 5,400 by the year's end, Defense Secretary Ash Carter admitted to Congress in July that only about 60 were trained.

That first class of 54 rebels disintegrated after deploying back into Syria, after being attacked by Al Nusra Front.

Earlier this month, U.S. Central Command commander Gen. Lloyd Austin III told Congress that only "four or five" of that group remained in the program. The Pentagon later revised that to nine.

About a week later, the Pentagon announced that approximately 70 more had deployed back into Syria, but pictures and claims began surfacing on social media that some had turned over their equipment to Al Nusra Front.

The Pentagon strenuously denied those reports, only to admit a few days later that they were correct.

On Monday, a Democratic senator and skeptic of the program called for the administration to suspend it.

"I am grateful for the work that has been put into trying to make this program successful," said Sen. Chris Murphy Christopher (Chris) Scott MurphyDemocratic senator calls for 'more flexible' medical supply chain to counter pandemics The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon GOP chairman to release interim report on Biden probe 'in about a week' MORE (D-Conn.), ranking member of the Senate Foreign Relations Committee's Subcommittee on the Near East, South Asia, Central Asia and Counterterrorism.

“But for those of us who opposed the Syria train and equip program from the start, our predictions that our assistance would end up aiding mortal enemies of the U.S. like al Qaeda are now coming true," he said.

The administration announced the creation of the program last year, which aimed to build a ground force to take on ISIS and supersede the need to send in U.S. forces. Congress authorized the program in September and provided $500 million for the program in December.

The administration has requested $600 million for the program in 2016.