The U.S. military has begun the process of withdrawing troops from Syria, a U.S. defense official confirmed to CBS News on Friday, saying it was expected to take between 90 and 120 days. The official told CBS News senior national security correspondent David Martin that equipment had begun moving out earlier this week, CBS News reported.

America's operations against the Islamic State of Iraq and Syria (ISIS) in the country were to continue during the withdrawal process. 

Col. Sean Ryan, spokesman for the coalition fighting ISIS, confirmed earlier in the day to The Associated Press that "the process of our deliberate withdrawal from Syria" was underway. 

"Out of concern for operational security, we will not discuss specific timelines, locations or troops movements," he said in a statement emailed to The Associated Press.

The Britain-based Syrian Observatory for Human Rights, which monitors the conflict in Syria through a network of activists on the ground, said the withdrawal began Thursday night. It said a convoy of about 10 armored vehicles, in addition to some trucks, pulled out from Syria's northeastern town of Rmeilan into Iraq.