Militants linked to Islamic State swept through a southern Philippine city, beheading a police chief, burning buildings, seizing a Roman Catholic priest and his worshippers and raising the black flag of Isis, regional authorities have said.

Axar.az reports citing the Guardian.

President Rodrigo Duterte had declared martial law across the southern third of the country – where Marawi city is located – and warned on Wednesday that he may expand it nationwide.

At least 21 people were killed in the fighting, officials said.

As details of the attack in Marawi emerged, fears mounted that the largest Roman Catholic state in Asia could join a growing list of countries grappling with the spread of influence from Isis in Syria and Iraq.

The violence erupted on Tuesday after the army raided the hideout of Isnilon Hapilon, a commander of the Abu Sayyaf militant group that has pledged allegiance to Isis. He is on Washington’s list of most-wanted terrorists with a $5m (£3.9m) reward for information leading to his capture.