U.S. Special Forces and FBI agents are in Syria searching for the remains of three Americans executed by ISIS and one woman who died while in captivity of unknown causes, according to a report from ABC News.

The effort to find the remains of the Americans was precipitated because of information gained from two high profile ISIS members that were recently captured. The Department of Defense and FBI told the International Business Times they had no comment on the searches.

The people whose remains are being sought are journalists James Foley and Steven Sotloff and aid workers Abdul-Rahman (Peter) Kassig and Kayla Mueller. Foley, Sotloff and Kassig were all beheaded by ISIS in 2014. The terrorist group videotaped their deaths and released them on the internet. Mueller was killed in 2015 — ISIS claimed she was killed by a coalition bombing by a Jordanian warplane. U.S. and Jordanian officials said there was no proof of the claim.

The two ISIS members captured were Alexanda Kotey and El Shafee Elsheikh, part of a four-person British contingent of the terrorist group nick-named “The Beatles.” The two men are believed to have been a part of the beheadings and torture of Western captives. The men were captured by American-backed Syrian Democratic Forces and are being interrogated by U.S. officials.

The leader of the “The Beatles,” Mohammed Emwazi, dubbed “Jihadi John,” was killed in 2015 by a drone strike. The other member, Aine Davis, was captured in Turkey in 2017.

The captured men are reportedly being questioned for information on the whereabouts of the buried remains of the killed hostages.

“I am grateful for all these efforts but bringing these two jihadists to justice gives us more hope and solace than the return of Jim's remains,” James Foley’s mother Diane told ABC News.

U.S. and coalition forces continue to fight ISIS in Syria and Iraq. The U.S. and its partners have sustained a number of air bombings in the region. ISIS has been rooted out of a majority of the territory it controlled, but still persists in the region.

A seven-year-long civil war in Syria allowed ISIS to fester in the country and create stronghold there, including its de facto capital, Raqqa. U.S. forces in the area are looking to stabilize the region to prevent any lapses back into ISIS control.