MANILA - Hundreds of Muslim militants linked to the Islamic State in Iraq and Syria (ISIS) attacked a military outpost and later occupied a school early on Wednesday (June 21) in Pigcawayan town, some 190km south of Marawi city where government troops and another group of extremists have been clashing for a fifth week.

Unconfirmed reports said at least eight civilians had died, and that some pupils were taken as hostages.

Chief Inspector Realan Mamon said some 300 fighters of the Bangsamoro Islamic Freedom Fighters (BIFF) stormed Pigcawayan at around 5am, in North Cotabato province, 900km south of the capital Manila.

They first attacked a military outpost in Malagakit district at dawn, and then retreated to a primary school there when army reinforcements arrived.

Later reports said the militants burned the school and had fled with their hostages.

Chief Insp Mamon, the Pagcawayan police chief, said the attack could be meant to divert military resources now used in Marawi.

About 500 militants from the Maute and Abu Sayyaf groups stormed Marawi on May 23 in an audacious bid to turn this lakeside city into an ISIS "province". They have since managed to hold on to four districts, despite heavy assaults from an entire army brigade.

Solicitor-General Jose Calida earlier tagged the BIFF, and the Maute and Abu Sayyaf groups, as among at least 20 ISIS-linked groups in the war-torn southern island group of Mindanao.