France is accelerating plans to end its military commitment in Syria and is considering airlifting captured foreign ISIS fighters out of the country, fearing that the precipitous American withdrawal of forces from the battlefield will leave liberated areas unstable and make it impossible to contain the prisoners.

In the wake of President Donald Trump’s sudden announcement in December that he was pulling American forces out of Syria, a senior French official tells NBC News the country is scrambling to adjust its military posture in anticipation of a power vacuum in northeastern Syria as it carries on fighting against the Islamic State. Of critical concern to French military planners is implementing a plan to deal with captured ISIS fighters and get them to get of the country before a U.S. withdrawal.

In an interview with French television BFMTV Tuesday, Interior Minister Christophe Castaner said he “couldn’t mention specifics” when asked if France was planning to transfer as many as 130 ISIS fighters to French soil.

Although France’s President Emmanuel Macron lambasted Trump for his decision last month to withdraw from Syria, French officials have been publicly cautious in commenting on how the withdrawal will affect their operations against the former caliphate.

But behind the scenes, they are dismayed and “deeply worried.”

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“American troops have made it clear that they are pulling out and that they received no warning in advance,” the French official said. “Since then, we’ve been working around the clock to plan for this American pull-out and how it will affect French military operations in Syria.”

More than 3,200 French military personnel have operated in Syria as part of Operation Chammal, the French campaign against ISIS. French special operations forces work closely with American, British and other allied units in both Syria and Iraq.

The French government announced two weeks ago it is committed to keeping troops in Syria and Iraq for the rest of the year, but the senior official admitted France does not think it can maintain a sustained military presence in the country without U.S. support. The official said France was in “close communication” with Washington about how to proceed.

One of the key concerns for France and other countries are the hundreds, if not thousands, of foreign nationals who flocked to the Islamic State and fought on its behalf. Hundreds of such foreign nationals have been captured on the battlefield by the U.S. and its allies, including France.

What to do with these detainees and returning fighters, or “retournees” as they are known in French, has been a central preoccupation of French counterterror officials.

Of the 22 successful terror attacks in France since 2012, 97 percent were carried out by individuals known to have been radicalized, or otherwise known to police, according to Olivier Guitta, the managing director of GlobalStrat, a risk management firm that studies terrorism. Many of these have been retournees.

“Syrian Democratic Forces are currently holding foreign terrorist fighters, including French nationals, in northeastern Syria,” said Agnès Von Der Mühll, a foreign ministry spokesperson. She would not confirm the number of detainees, however, adding that in light of “American decisions,” the French government was “exploring all options in order to prevent these potentially dangerous individuals from escaping or dispersing.”

The French interior minister said that all of the detainees will be charged upon arrival on French soil. The minister said that each detainee would be charged individually depending on the evidence of crimes they are alleged to have committed — including murder, kidnapping and torture. Previously, prosecutors have successfully convicted some French ISIS members of “association with criminal terrorist activity.”

Although the bulk of the captured fighters are believed to be French nationals, many have yet to be positively identified and have only provided “noms de guerre,” or aliases.

Law enforcement agencies from around the world have been working to share information about captured fighters and terror suspects, often through Interpol, the global law enforcement organization that is headquartered in France.

Interpol has been central to coordinating global efforts to combat terrorism, and now maintains and disseminates a database of 40,000 profiles of “Foreign Terrorist Fighters,” up from just 13 in 2012.