Malaysia vowed to beef up security Monday in an eastern state where at least 26 people have been reported killed after a bizarre invasion by Philippine followers of a self-styled sultan.
Prime Minister Najib Razak, who is under pressure over Malaysia's worst security crisis in years, has authorised a "doubling" of police and armed forces deployed in the tense state of Sabah on Borneo island.
"An additional two army battalions have been dispatched to Sabah," Najib, who has vowed to root out the intruders, was quoted as saying by state news agency Bernama.
Malaysians have been shocked by the militant incursion, which began when an estimated 100-300 people landed on the shores of Sabah on February 12, claiming the state for the heir to a former Philippine sultanate.
The armed intrusion has embarrassed Malaysian premier Najib -- who must call elections by June -- by exposing lax border security and fuelling perceptions of lawlessness and huge illegal immigration in Sabah.
A tense stand-off between the intruders and security forces who have them pinned down in the farming village of Tanduo erupted in a bloody firefight Friday that left 12 gunmen and two police officers dead.
Another gun battle erupted in Semporna, 300 kilometres (190 miles) away, on Saturday night, dramatically escalating tensions and raising the overall toll of reported dead to at least 18 militants and eight police officers.
It remains unclear whether the Semporna confrontation was resolved or is ongoing.
Followers of the 74-year-old Manila-based Islamic leader, Jamalul Kiram III, say the gunmen are ready to die to defend his claim to Sabah, which was once controlled by the now-defunct sultanate.
The fresh weekend clash in Semporna -- and a police claim that they were pursuing yet another group of gunmen in a nearby town -- has sparked fears of further infiltration by armed Filipinos along the coast.
The exact identities of the gunmen remains a mystery, but Malaysian armed forces chief Zulkifeli Zin told a press conference in Sabah on Sunday that the intruders appeared to have combat experience.
Their "insurgency guerrilla technique is quite good," he was quoted saying.
Sabah has seen previous smaller-scale cross-border raids from Islamic militants and other bandits from the adjacent southern Philippines, which has suffered for decades from a campaign by Muslim insurgents.
Malaysian authorities have not clearly said whether the different armed groups in the current troubles are related, instead issuing calls for calm, saying the situation is under control.
The Star newspaper has reported, however, that thousands of families fled Semporna in panic.
Sabah's police chief Hamza Taib was quoted by Malaysian press saying an armed man in commando gear was killed by angry villagers near Semporna. It was not clear whether he was one of the six militants reported killed in Saturday's shooting.
The Sulu sultanate's power faded about a century ago but it has continued to receive nominal Malaysian payments for Sabah under a lease deal inherited from European colonial powers.