BEIRUT (Reuters) - U.S.-backed forces on Thursday fully encircled the Islamic State-held city of Raqqa after closing the militants’ last way out from the south, the Syrian Observatory for Human Rights monitoring group said.

The Syrian Democratic Forces (SDF), an alliance of Kurdish and Arab fighters that launched a long-anticipated assault on the Islamists’ de facto Syrian capital this month, had earlier said they were on the point of cutting off Raqqa’s last exit.