Russian-backed Syrian regime forces on Friday broke into the eastern town of Mayadeen, one of the Islamic State group's last bastions in the country, a monitor said.

"With support from Russian aviation, regime forces entered Mayadeen and took control of several buildings in the west of the town" in the eastern province of Deir Ezzor, Rami Abdel Rahman, head of the Britain-based Syrian Observatory for Human Rights, told AFP.