BEIRUT (AP) — A Syria war monitor and a U.S. official say U.S.-backed fighters have seized the last road into Raqqa and are moving toward the river south of the city, tightening a siege on the militant de-facto capital.

A spokesman for the U.S.-led coalition told The Associated Press the Kurdish-led Syrian Democratic Forces are now in control of all high speed routes into Raqqa and are moving toward the Euphrates River. "This would completely encircle the city and has been the SDF plan from the start," Col. Joe Scrocca, spokesman for the U.S-led coalition said in emails to the AP.

The Britain-based Syrian Observatory for Human Rights said a component of the SDF have completed the siege around the city after seizing villages across the river, describing it as a "strategic" advance.