Turkish-backed Syrian Arab forces have deliberately released ISIS prisoners amid Turkey's invasion into northern Syria, two US officials told Foreign Policy.

This report contradicts Trump's suggestion Kurdish forces released prisoners to draw the US back into the region following his controversial decision to pull troops out.

Trump's decision to abandon the Kurds, who bore the brunt of the campaign against ISIS, has sparked widespread criticism — including rare blowback from congressional Republicans.

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President Donald Trump on Monday suggested Kurdish forces had released ISIS-related prisoners to bait him back into northeast Syria, but two US officials say it was actually Turkish-backed forces with ties to extremism that released the detainees, Foreign Policy reported.

The Free Syrian Army, a group of Arab militants in Syria backed by Turkey, is reported to be deliberately releasing ISIS detainees amid a Turkish military operation targeting the Kurds in northeast Syria.

The Pentagon on Monday afternoon also released a statement from Secretary of Defense Mark Esper that blamed Turkey, not the Kurds, for the release of ISIS detainee es.

"Despite the opposition and repeated warnings from the US and the international community, Turkish President Erdogan ordered a unilateral invasion of northern Syria that has resulted in widespread casualties, refugees, destruction, insecurity, and a growing threat to US military forces," Esper said.

He added: "This unacceptable incursion has also undermined the successful multinational 'Defeat ISIS' mission in Syria, and resulted in the release of many dangerous ISIS detainees."

Until recently, Kurdish forces were allied with the US against ISIS. The Kurdish-led Syrian Democratic Forces played a crucial role in crushing ISIS's so-called caliphate, and lost roughly 11,000 fighters in the process.

But Trump abruptly abandoned the Kurds last Sunday when the White House announced the US would be pulling troops from northeast Syria, a move that paved the way for the Turkish military incursion in the region.

Read more: The US shared intelligence with Turkey that may have helped it target the Kurds in Syria

The Turkish assault has occurred in concert with reports of atrocities committed by Turkish-backed Syrian Arab fighters like the Free Syrian Army.

Trump's Syria retreat has been widely condemned, including by congressional Republicans, and viewed as a betrayal of the Kurds given they bore the brunt of the US-led campaign against ISIS. Many in Washington have expressed concerns that the move opens the door for the resurgence of ISIS by creating a security vacuum.

Kurdish forces have been detaining roughly 11,000 ISIS fighters, including approximately 2,000 foreign fighters, but they've been forced to divert their attention to the Turkish invasion.

After it was reported that hundreds of ISIS-related prisoners had escaped a prison camp in northern Syria over the weekend, Trump on Monday tweeted, "Europe had a chance to get their ISIS prisoners, but didn't want the cost. 'Let the USA pay,' they said...Kurds may be releasing some to get us involved. Easily recaptured by Turkey or European Nations from where many came, but they should move quickly."

There's no evidence to support Trump's suggestion Kurdish forces released ISIS prisoners, and a senior US official told CNN that "falsely claiming that the SDF Kurds are letting ISIS prisoners out of prison is wrong because they are the people that defeated ISIS, wrong because they are currently risking their lives to defend our forces."

On Friday, US troops in Kobani came under fire from Turkish artillery. The troops were unharmed, but some reports suggest that this was a deliberate effort to push US forces out of the region.

Meanwhile, the Pentagon over the weekend announced the US is moving to withdrawal about 1,000 remaining troops from northern Syria on top of the small group that's already been relocated.

"We have American forces likely caught between two opposing advancing armies, and it's a very untenable situation," Defense Secretary Mark Esper told CBS's "Face the Nation" on Sunday.