Unidentified gunmen have kidnapped another Indonesian sailor in the Sulu Sea where numerous seafarers have been abducted by Islamist extremists in recent months, officials said Sunday.

The kidnapping took place Wednesday off the northeast of Sabah state on the Malaysian side of Borneo island, Indonesia's ambassador to Malaysia said.
"(The vessel) was intercepted by a boat carrying four armed men," ambassador Herman Prayitno told AFP.
The kidnappers took the Indonesian captain after failing to get the 10,000 ringgit ($2,500) they demanded, Prayitno added. They released the two other crew members, an Indonesian and a Malaysian.
Indonesia's foreign ministry said it was still trying to find out which group was responsible.
Malaysia's marine police chief Abdul Rahim Abdullah told AFP authorities were questioning the two crew members from the boat about the case.
The kidnapping is the latest in a string of incidents in the Sulu Sea, where groups of armed men have ambushed fishing vessels and seized Malaysian and Indonesian citizens for ransom.
Ten other Indonesians kidnapped in recent months by the Philippine Abu Sayyaf extremist group are still being held.
Jakarta has banned Indonesian-flagged vessels from sailing to the Philippines and pushed for joint maritime patrols in the waterway.
A handful of Malaysian sailors have also been kidnapped this year.
The Abu Sayyaf, who are based on remote and mountainous southern Philippine islands, beheaded two Canadian hostages this year after their multi-million-dollar ransom demands were not met. In 2015 they killed a Malaysian hostage.
The group is a loose network of a few hundred Islamist militants, formed in the 1990s with seed money from Osama bin Laden's Al-Qaeda network.