JAKARTA:  militants in the southern Philippines boarded an Indonesian tugboat and abducted seven of 13 crew members in a third such attack in the volatile region, the Indonesian foreign minister said Friday.

The crewmen were believed to be taken by two separate groups to a jungle camp in Sulu, a predominantly Muslim province about 950 kilometres (590 miles) south of the Philippine capital, Manila, Foreign Minister Retno Marsudi told a news conference in Jakarta.

Jolo island in Sulu province is a stronghold of militants from the Abu Sayyaf group, notorious for ransom kidnappings and beheadings of hostages.

"This third incident absolutely cannot be tolerated," Marsudi said. "The government will do everything possible to ensure the release of all those hostages. The safety of the seven Indonesians will be prioritised."

She said that the government received confirmation that six of the 13 crew members of the tugboat that was towing a coal barge were freed with the vessel and on their way to Indonesia.

Filipino militants held 14 Indonesians among more than 20 hostages after raiding tugboats in separate incidents in late March and early April. The Indonesians were freed last month following reports that a ransom was paid, but the Indonesian government denied it gave money.

After meeting security ministers and military and intelligence chiefs on Friday, Marsudi said that Indonesia extended a moratorium on coal exports to the region until the Philippine government can guarantee security for coal barges in its waters.

She said that Indonesia supplies more than 90 percent of coal to the southern Philippines.

Foreign ministers and military chiefs from Indonesia, Malaysia and the Philippines agreed in a recent meeting to boost maritime security and take possible coordinated actions, including sea and air patrols, to stem a wave of kidnappings.