Some 17 school children and their principal, who were taken hostage by an armed group in south Philippines, have been released.

But 57 other adult hostages remain in captivity, authorities have said.

The abduction was carried out in the troubled southern region of Mindanao early on Thursday by what authorities described as former members of a civilian militia known as the "Perez group".

Philippine officials said that government negotiators had put off until Friday talks to secure the release of the remaining 57 people.

"Negotiations are ongoing. We are trying to find out how the others can be released," Lino Calingasan, regional police chief, told Reuters news agency.

"It is a good signal, that they are willing to negotiate. We are hoping this will be resolved peacefully."

Some officials said they could have taken hostages because they were being pursued by police after a gunbattle with a rival tribal group on Wednesday.

Al Jazeera's Marga Ortigas, reporting from Manila, said it was unclear what the group wanted although police say there is no political or religious motive for the kidnapping.

She said the group was known to local police having been armed by the Philippines government a decade ago to fight against communist insurgents in the area.

Extortion

The raid was carried out less than three weeks after a massacre in a nearby province in which 57 people were killed, throwing an unwelcome spotlight on the Southeast Asian nation and raising tensions ahead of presidential elections next year.

Our correspondent said that last month's massacre and Thursday's kidnappings had many Filipinos questioning whether it was a good idea to arm these groups in the first place, when the army should have been fighting the insurgents.

"People are saying this was a monster the government had created, and it's now come back to bite them," she said.