U.S.-backed militias said they had defeated the Islamic State in its former capital Raqqa on Tuesday, raising their flags over the jihadi group's last footholds in the city after a four-month battle.

The fighting was over but the alliance of Kurdish and Arab militias was clearing the stadium of mines and any remaining militants, said Rojda Felat, commander of the Raqqa campaign for the Syrian Democratic Forces (SDF).

A formal declaration of victory in Raqqa will soon be made, once the city has been cleared of mines and any possible IS sleeper cells, said Talal Silo, the SDF spokesman.