Search and rescue groups have found bodies of three unidentified institutions, according to anonymous sources.
A Katari mission began to search for the remains of American hostages killed by armed groups in ISIS, Reuters news agency reported.
The international search and rescue team in Qatar began a search on Wednesday, with the help of several American nationals who wanted to remain anonymous, according to the news agency.
According to sources, the group has so far found three unidentified bodies. A Syrian security source told Reuters that the mission focused on locating the body of aid worker Peter Kassig, who beheaded in 2014 in Dabiq, northern Syria.
American aid workers Kayla Mueller, along with American journalists James Foley and Steven Sotloff, are other Western hostages killed by Isil. Foley and Sotloff were confirmed in 2014. Mueller's killings were confirmed in 2015.
"We thank anyone who took on this task and risked his life in some cases trying to find the bodies of Jim and other hostages," said Diane Foley, the mother of James Foley. "We thank everyone who has been involved in this effort."
The Katari mission is underway as President Donald Trump prepares to visit Doha and other Arab Gulf next week, Syria's new government seeks to alleviate sanctions imposed by the United States.
Washington, along with other Western governments, said it would wait for the new authorities to exercise their powers and ensure that human rights are before any sanctions are filed.
Last month, the UK lifted sanctions on 12 Syrian government entities, including the Ministry of Defense and the Ministry of Home Affairs and the General Intelligence Agency.
ISIL once controlled vast fragments of Syria and Iraq, ruled millions. When power peaked between 2014 and 2017, it was imprisoned many people, including Western hostages, and released videos of the killing.
The alliance of more than 80 countries led by the United States fought against ISIL in September 2014.
The war against the group officially ended in March 2019, when fighters from US-backed Kurdish-led Syrian Democratic Army occupied the eastern Syrian town of Baghouz, the last part of the Land Isil.
Kathari Prime Minister Sheikh Mohammed bin bin Jassim al Thani and Secretary of State Mohammed Al Khulaifi discussed plans for the Qatari mission during his visit to Washington in April - the trip also aimed at Trump's visit to Qatar (Truck).
Another person familiar with the issue said the U.S. government has long been committed to finding the remains of murdered American nationals and has previously had multiple “a very specific area of effort with U.S. government officials in Syria.”
The report said the person did not specify it. But the United States has deployed hundreds of soldiers in northeastern Syria, who continue to hunt down the remnants of ISIL.
The man said the remains of Kasig, Sotlov and Foley were likely located in this part of the country. The person added that Mueller's case was different because she was detained by ISIL leader Abu Bakr al-Baghdadi.
Two ISIL members, both former British citizens, are serving sentences in the United States as part of a cell called the Beatles, a hostage.