Muslim extremists supporting the Islamic State group have freed eight fellow militants in a daring attack that also allowed 15 other inmates to escape from a provincial jail in the southern Philippines.

Police say about 20 heavily-armed fighters of the Maute militant group stormed the Lanao del Sur provincial jail in Marawi city before nightfall Saturday, disarmed the guards and rescued their eight comrades, including three women. The attackers also seized two rifles from guards.

Police said Sunday the eight militants were arrested by army troops and police when they were caught with a homemade mortar shell in a van in Lanao del Sur's Lumbayanague town.

The Maute group is a new band of armed Muslim radicals, who have pledged allegiance to the Islamic State group.