WASHINGTON - U.S.-backed forces in Syria holding thousands of Islamic State fighters following the collapse of the terror group's caliphate are starting to get help to make sure detained fighters stay behind bars.

U.S. and coalition officials confirm aid is being sent to Syrian Democratic Forces to make sure they can accommodate upwards of 7,000 IS fighters who have been in custody since the fall of the group's final stronghold in Baghuz last month.

"The coalition is assisting with the repair and refurbishment of some prison facilities," Pentagon spokesman Cmdr. Sean Robertson told VOA. "This is an international problem that requires an international solution."

SDF officials initially said more than 5,000 IS fighters had been captured or surrendered in the more than a month leading up to the group's territorial defeat in the northeastern town of Baghuz. According to U.S. officials, that number then rose even higher in the final days of the campaign.

FILE PHOTO: Prisoners that are said to be Islamic FILE - Prisoners that are said to be Islamic State fighters by Syrian Democratic Forces fighters, are pictured north of Raqqa, Syria, March 8, 2017. FILE - Prisoners that are said to be Islamic State fighters by Syrian Democratic Forces fighters, are pictured north of Raqqa, Syria, March 8, 2017.

Even before IS's territorial defeat, some officials voiced concern that the SDF's detention capabilities were being pushed to the limit.

"They are going to need significant help," a senior U.S. defense official warned in early March.

"They've done incredible work being able to build a prison system out of essentially nothing," the official said at the time. "They'll basically take a facility, a school or something like that, and turn it into a holding facility — not sustainable, but something that's good enough for now."

Just how much the coalition's prison repair and refurbishment efforts will help ease the crunch is unclear. Still, there is some hope that the strain on the SDF is slowly being reduced in other ways.

U.S. officials estimate roughly 3,000 of the IS prisoners in SDF custody are from Iraq. Officials in Baghdad have indicated they are willing to take many of those fighters back in order to prosecute them under Iraqi law for crimes against Iraq.

Yet there are still questions about the fate of an estimated 1,000 foreign fighters now languishing in SDF custody.

"Repatriating foreign terrorist fighters to their countries of origin remains the best solution to prevent them from returning to the battlefield," Robertson said.So far, that has proved to be a difficult sell to a number of countries whose governments have balked at taking back any IS fighters.

FILE PHOTO: A Syrian Democratic Forces fighter sta FILE - A Syrian Democratic Forces fighter stands near who he said were Islamic State fighters held prisoners, north of Raqqa, Syria, March 8, 2017. FILE - A Syrian Democratic Forces fighter stands near who he said were Islamic State fighters held prisoners, north of Raqqa, Syria, March 8, 2017.

In the meantime, concerns are growing that strained SDF prison facilities could soon become a target for IS insurgent cells and sleeper cells that have grown increasingly active in recent weeks.

"Of course," Bassam Ishak, a co-chair of the Syrian Democratic Council in Washington — part of the SDF's political wing — said of the resurgent IS threat. "For that, we will need a different kind of support. We have asked the U.S. for that as (the territorial campaign) was winding down."

Specifically, SDF officials would like to see more U.S. troops remain on the ground, arguing that the airstrikes that were so effective in helping roll back IS's caliphate will be of limited use against small cells of fighters who are hiding, at times, among the civilian population.

They have also requested more help from U.S. intelligence, suggesting the U.S. establish a base of sorts near at least one of the prison facilities.

To this point, there are few indications U.S. officials are likely to agree to those requests. Publicly, U.S. officials have said they intend to leave no more than a couple of hundred U.S. troops in Syria, part of a possible residual force of about 1,500 troops from coalition countries.