Manila: Lawmakers on Saturday voted to extend martial law in the southern Philippines, with no end in sight to a battle with a Daesh-aligned force in Marawi.

A total of 261 legislators out of more than 300 agreed to extend military rule until December 31, approving President Rodrigo Duterte's request.

Duterte declared martial law on May 23 following a bloody siege of the southern city of Marawi by Daesh-aligned militants.

The country's constitution allows the president to impose martial law for up to 60 days, enabling him to "call out the armed forces to prevent or suppress lawless violence, invasion or rebellion".

Beyond two months, the president can extend it "for a period to be determined by the Congress".

In May, Duterte said he had made the move to stamp out an attempt by militants, including foreign fighters, to establish a Daesh caliphate on Philippine territory.

"He also explained clearly his fear that terrorism might slowly spread throughout Mindanao and eventually the country," Senator Sherwin Gatchalian.

Security forces have been conducting a US-backed offensive to root out the gunmen, using air strikes and artillery fire.