Rayburn, who replaced James Jeffreys as the U.S, envoy and top diplomat for the coalition against the Islamic State (ISIS) in November, is stepping down due to "policy and personnel differences" with the incoming Joe Biden administration, the sources said.

It is unclear how much of President Donald Trump's policy carried out by Jeffreys and then Rayburn will be continued under Biden. The president-elect was critical of Trump's decision to withdraw U.S forces from Syria at Turkey's request in Oct. 2019 and so were important members of his team including his nominees for Secretary of State and National Security Advisor, Antony Blinken and Jake Sullivan.

Biden recently named Brett McGurk, one of Rayburn's predecessors, to his National Security Council as coordinator for the Middle East and North Africa. McGurk resigned in December 2018 after Trump's first attempt to leave Syria and he has been a frequent critic of Turkey, who opposes U.S support for the Syrian Kurdish militants that it sees as terrorists.

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