The Kurdish-led Syrian Democratic Forces (SDF) said on Sunday they had worked with the United States on a "successful" operation against Islamic State, in an apparent reference to reports that IS leader Abu Bakr al-Baghdadi is believed to have been killed in a U.S. military operation in Syria."Our strong and effective operations once again confirm our strength and determination to go after (Islamic State)," the head of the SDF's media office, Mustafa Bali, said on Twitter in Arabic. SDF commander Mazloum Abdi said on Twitter an "historic, successful operation" resulted from joint intelligence work with the U.S.The SDF is an alliance in north and east Syria which worked with the U.S.-led coalition against Islamic State. But U.S. President Donald Trump announced the withdrawal of American troops from Syria two weeks ago ahead of a cross-border offensive by Turkey against the Kurdish presence there."We continue to work with our partners in the global coalition in the fight against ISIS terrorism," Bali added in English.