Ten Indonesian sailors have been kidnapped in Philippine waters by Islamic militants who have demanded a ransom for their release, an official said Tuesday.
The crew were travelling on two boats that were transporting coal from Borneo island to the Philippines when they were hijacked, said Indonesia's foreign ministry spokesman Arrmanatha Nasir.
It is not clear when the vessels -- a tugboat and a barge -- were hijacked but the boats' owners received a ransom call from someone claiming to be from the Abu Sayyaf militant group on Saturday, Nasir said.
Abu Sayyaf is a Philippines-based Islamist group notorious for bombings and kidnappings, which has pledged allegiance to the Islamic State group.
"The hijackers demanded a ransom from the owners of the boat. Since March 26, the hijackers have contacted the owners twice," Nasir told reporters, without elaborating on how much had been demanded for the crew's release.
It is unclear where the barge Anand 12 and the crew are being held by the kidnappers but the tugboat Brahma 12 had been released to the Philippine authorities, he added.
The Indonesian foreign ministry is working with the Philippines foreign ministry on the case, Nasir said.
"Our current priority is the safety of the 10 citizens who were taken hostage," he said, adding their families had been informed.
There was no immediate confirmation from authorities in the Philippines.
But the Philippine military chief, General Hernando Iriberri, flew to the main army base in the south of the country to check on the situation and discuss what steps should be taken, his spokesman Brigadier General Restituto Padilla told AFP.
The Philippine government has repeatedly said it has a "no-ransom policy". But parties linked to foreigners held hostage by the Abu Sayyaf often pay to win their release.