FILE - Fighters from the Islamic State group parade in Raqqa, north Syria, June 30, 2014. Former British spy chief says militants more than doubled the recruitment of foreign fighters to as much as 31,000 over the past 18 months.
FILE - Islamic State fighters parade in Raqqa, Syria, June 30, 2014. A former British spy chief said militants at that point had more than doubled the recruitment of foreign fighters, to as much as 31,000, over the previous 18 months.

An American suspected of fighting with the Islamic State terror group in Syria is back in the United States, where he is expected to be charged with and tried for terrorism-related crimes. 
U.S. defense officials confirmed the transfer of the suspect Thursday, saying U.S. troops assisted in bringing the U.S. national back home for prosecution. 
According to a Pentagon statement, the suspect "was previously held by Syrian Democratic Forces as a suspected member of ISIS." It referred other questions to the Department of Justice. Justice Department officials said they were aware of the transfer, first reported by CNN, but declined to comment. 

FILE - In this picture taken July 21, 2017, Kurdish soldiers from the Anti-Terrorism Units, background, stand in front a blindfolded suspected Islamic State member from Turkey at a security center, in Kobani, Syria.

Holding foreign fighters 
Since the collapse of the Islamic State's physical caliphate in Syria in March, U.S.-backed Syrian Democratic Forces have been holding an estimated 2,000 foreign fighters from more than 50 countries in makeshift prisons. In addition, the SDF has processed tens of thousands of civilians linked to IS, including the wives and children of the foreign fighters. 
There are no official estimates of how many of the IS prisoners were U.S. citizens or residents. But in comments to VOA this past June, Kurdish officials suggested more Americans were in custody. 
"It's up to the U.S. government whether it wants to take back more of its citizens held by our forces," said Kamal Akif, a spokesman for the Kurdish-led administration in northeast Syria. 
Independent research by George Washington University's Program on Extremism has identified 79 U.S. citizens or residents who traveled to Syria or Iraq to join extremist groups since 2011, 75% of whom aligned themselves with IS.
In June, the U.S. repatriated two American women accused of joining IS, along with their six children. It is unclear whether the women will face charges. 

Four to face charges
Four other U.S. citizens — three men and one woman — who left the country to join IS have also been brought back to face charges. 
Most recently, the U.S. brought back Warren Christopher Clark in January. 
Last July, the U.S. repatriated Ibraheem Musaibli and Samantha ElHassani from Syria. Musaibli, a resident of Dearborn, Michigan, was charged with joining IS in 2015. ElHassani was charged with providing material support to IS and with helping other individuals join the terror group. Her four children, who also came back with her from Syria, were placed in the custody of officials with the U.S. state of Indiana. 
In June 2017, the U.S. brought back Mohamad Jamal Khweis of Alexandria, Virginia. Khweis, who was found wandering in Iraq by Kurdish peshmerga forces, was found guilty of providing material support to IS. 

Graphic of Americans who have repatriated from Syria

Western nations' fighters 
To help ease the burden on the SDF, the U.S. has been pushing for Western nations especially to repatriate their foreign fighters and prosecute them. 
But at times, Washington has balked at taking back some of those with ties to the U.S., such as American-born Hoda Muthana, 24, whose father was a Yemeni diplomat around the time of her birth. 
U.S. officials have said they continue to work to verify the U.S. citizenship of those individuals in the conflict zone on a case-by-case basis. 
U.S. counterterrorism officials estimate that more than 45,000 foreign fighters flocked to Syria and Iraq following the start of the Syrian civil war, including 8,000 from Western countries. 
An independent estimate by researchers at the International Center for the Study of Radicalization, just published by the Combating Terrorism Center's CTC Sentinel, estimates IS still counts almost 53,000 foreigners among its ranks in Syria and Iraq, including more than 6,900 foreign women and up to 6,600 foreign children.