Islamic State group militants on Saturday killed 20 members of pro-regime forces in an attack on a Syrian hospital in the eastern city of Deir Ezzor, a monitoring group said.

"IS group attacked Al-Assad hospital at the city's eastern entrance, killing at least 20 soldiers and allied fighters," said Rami Abdel Rahman, director of the Britain-based Syrian Observatory for Human Rights.

He said the attack sparked clashes in which six militants were also killed.