A senior Republican senator on Sunday warned U.S. President Donald Trump against pulling U.S. troops from Syria, saying it would lead to a resurgence of Islamic State and increased Iranian sway over the Syrian government in Damascus.

"It'd be the single worst decision the president could make," Republican Senator Lindsey Graham, a member of the Senate Armed Services Committee, said on the "Fox News Sunday" program.

"We got ISIL on the ropes. You want to let 'em off the ropes, remove American soldiers," Graham said, using an acronym for Islamic State.