Ten Indonesian sailors have been kidnapped in Philippine waters by Islamic militants who have demanded a ransom for their release, a minister said Tuesday.
The crew were travelling on two boats that were transporting coal from Borneo island to the Philippines when they were hijacked, said Indonesian Foreign Minister Retno Marsudi.
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, she said.
Abu Sayyaf is a Philippines-based Islamist group notorious for bombings and kidnappings, which has pledged allegiance to the Islamic State group.
Marsudi said the hijackers had contacted the boats' owners twice since Saturday and had sought a ransom, but refused to say how much was demanded.
"Our priority is the safety of the 10 Indonesians who are being held hostage, we will keep working hard to save them," the minister told reporters, adding she had been in touch with her Philippine counterpart.
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, she said.
- High-profile kidnappings -
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.
Keith Loveard, a senior risk analyst at Concord Consulting in Jakarta, said it was surprising to hear Abu Sayyaf had abducted sailors from Indonesia, which has the world's biggest Muslim population.
"They have normally gone for tourists and other Filipinos," he told AFP. "If we assume for the moment these are probably Muslim sailors, they might have an easier time than otherwise."
Abu Sayyaf was founded in the 1990s with the help of late Al-Qaeda mastermind Osama bin Laden and has been blamed for some of the Philippines' worst terror attacks. It has been designated a terrorist organisation by the United States.
The group operates from remote jungle bases in the strife-torn southern Philippines and has also carried out a series of high-profile kidnappings in recent times.
Last year the militants beheaded a Malaysian man in the south of the country after abducting him from a seaside restaurant in Malaysia's Sabah state.
A Malaysian woman seized along with him was released after a ransom was reportedly paid.
The group also abducted two Canadian tourists, a Norwegian resort manager and a Filipina from yachts at a marina in the southern Philippines in September, and demanded a ransom of millions of dollars.
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.
In October 2014 the Abu Sayyaf claimed it received 250 million pesos ($5.3 million) in exchange for two German hostages it held captive for six months. Security analysts said a large ransom was paid.