KOTA KINABALU (THE STAR/ASIA NEWS NETWORK) - Police have launched a massive hunt for Royal Sulu Force (RSF) militants who are believed to be in Sabah state and trying to resume operations here.

Eastern Sabah Security Command (Esscom) personnel and a special police task force are busy tracking down known RSF militants and the others.

Sabah Police Commissioner Jalaluddin Abdul Rahman declined to give details of the operation or say how many of the militants are believed to be here.

"They are mainly in the east-coast areas, such as Semporna and Lahad Datu," he said at the monthly state police gathering at the Kepayan headquarters on Wednesday.

Two men who were killed by police in a shootout at the Penampang Baru township on Oct 30 turned out to be RSF militants, although they were initially thought to be robbers.

They were both Filipinos, aged 42 and 50, and one was a leader based in the state, Datuk Jalaluddin said.

"Both were illegal immigrants," he said, adding that one man had a false Malaysian identity card while the other had a Philippine passport.

Police believe the RSF militants are planning to cause trouble in Sabah, as well as raise capital through criminal activities, including robberies and kidnappings.

"They have links to the kidnap-for-ransom group led by the notorious Muktadir brothers," Datuk Jalaluddin said.

The brothers - Badong, Ali @ Brown and Nikson - are believed to be behind the spate of kidnappings in the state over the past few years and are high on the police wanted list.

RSF militants have been trying to re-establish themselves after their armed invasion into Tanduo, a village in Lahad Datu on Feb 12, 2013, failed.

The 200-strong gunmen were led by Raja Muda Azzimuddie Kiram, who was sent by his elder brother, the self-proclaimed Sulu Sultan Jamalul Kiram III, to "reclaim" Sabah.

Malaysian armed forces killed many of the militants in the following weeks but some, including Azzimuddie, managed to flee.

Jamalul died in October that year and nothing more was heard of his followers.

Who the key players are behind the RSF militants now remain unclear but some speculate that other pretenders to the Sulu throne may be involved and have recruited former Moro National Liberation Front (MNLF) members and others.

The MNLF is a separatist movement in the southern Philippines that wants an independent Islamic state.

Sabah police arrested six people, including a policeman and a navy personnel, recently for alleged involvement with the RSF.

Three are being detained under preventive laws while the others have been released.

A sea curfew, enforced in six districts on the east coast of Sabah in July, has just been extended to Nov 22.