WASHINGTON — The American-backed Syrian Democratic Forces captured two notorious British members of an Islamic State insurgent cell commonly dubbed "The Beatles" and known for beheading hostages, a U.S. military official said Thursday.

The official said that El Shafee Elsheikh and Alexanda Amon Kotey were captured in early January in eastern Syria. The two men are among four members of the IS cell that captured, tortured and beheaded more than two dozen hostages including American journalists James Foley and Steven Sotloff, and American aid worker Peter Kassig. The official spoke on condition of anonymity to provide details of the Syrian capture.

The State Department has imposed sanctions on both men. They are believed to be linked to the British terrorist known as Jihadi John, the masked IS militant who appeared in several videos depicting the graphic beheadings of Western hostages.

Their capture was first reported by the New York Times.

According to the U.S., Elsheikh traveled to Syria in 2012 and first joined al-Qaida's branch there, and then later joined IS. The State Department, in imposing sanctions on Kotey last year, said he likely engaged in executions and torture, including electronic shock and waterboarding, and recruited several British nationals to IS.

According to military officials, the two men represent just a small portion of the hundreds of foreign-born IS terrorists from a number of nations that SDF fighters have captured or killed since October 2017.

U.S. officials did not provide any other details of the capture, but said the U.S. government with its coalition partners on the disposition of detainees held by the SDF. They said those discussions are private and no additional information would be given.

Sotloff was kidnapped in August 2013 after crossing into Syria from Turkey. He was killed on Sept. 2, 2014, and a video was distributed around the world documenting his death. Foley, another American journalist, had been killed a month earlier by the Islamic State. Kassig was an American aid worker captured by Islamic State militants in 2013 while delivering relief supplies to refugees in Syria.