CEYLANPINAR, Turkey — Two Belgian ISIS fighters have escaped from a Kurdish prison after the Turkish offensive began in northeastern Syria last week, a Belgian security source and a separate Belgian parliamentary source told NBC News.

The sources, who agreed to speak on the condition of anonymity because they were not authorized to speak to the press, offered no further information.

The two Belgians are the first foreign fighters who NBC News has confirmed to have escaped during the weeklong conflict in northern Syria.

It is unclear in the chaotic, fast-moving conflict how many other fighters of the Islamic State militant group or members of their families may have escaped.

The Syrian Democratic Forces prison authority said at least five prisoners escaped from an ISIS jail outside Qamishli after projectiles from Turkey hit the prison yard Oct. 11, but did not give details on their nationalities. NBC News was unable to independently verify the claim.

Many of the group's fighters captured in northern Syria are in prisons guarded by Kurdish-led forces, while their families are in SDF-guarded camps.

The Syrian Democratic Forces have been a crucial U.S. ally in the fight against ISIS, but now feel abandoned by America and have turned to Syrian President Bashar Assad and Russian President Vladimir Putin to help deter a Turkish invasion.

Gen. Mazloum Kobani, commander of the SDF, said last week that the approximately 12,000 suspected terrorists in detention centers are now a “second priority” for his forces. Of the 12,000, some 2,000 are foreign fighters while the others are Iraqis and Syrians, Pentagon officials say.

Current and former intelligence officials have told NBC News that a sustained Turkish military operation against Kurdish forces in Syria would vastly increase the threat to Americans from ISIS, which remains intent on attacking the West.

Syrian refugees fleeing the Turkish incursion in Northern Syria wait to receive aid from the UNHCR and other International NGOs as more than 200 people arrive at the facility on Thursday in Dohuk, Iraq. Byron Smith / Getty Images

In one ISIS jail, which houses some 5,000 inmates, the warden told NBC News that if the conflict deteriorates, the SDF guards would have no choice but to leave and head for the front lines.

“If there was an attack on the prison, we'd lock all the doors and go to the areas that they are in to fight and protect northern Syria,” Sarhat Amudi said, referring to Turkish forces.

Erin McLaughlin and Mac William Bishop reported from Ceylanpinar, Turkey; Saphora Smith reported from London and Marc Smith reported from northern Syria.