Malaysia threatened to take "drastic action" against intruding followers of a self-proclaimed Filipino sultan who have vowed to dig in after a shootout that killed 14 people.
Twelve followers of the little-known Sultan of Sulu and two Malaysian security personnel were killed in Friday's firefight, police said on Saturday, as the more than two-week-old siege in a remote corner of Malaysia turned deadly.
Dozens of Filipinos have been holed up on Borneo island, surrounded by a massive Malaysian police and military cordon, since landing by boat from the nearby Philippines to insist the area belongs to their Islamic leader.
"We want them to surrender immediately. If they don't, they will face drastic action," Hamza Taib, police chief of the Malaysian state of Sabah where the drama was taking place, said.
He declined to provide details of what security forces had in store but his comments echoed growing Malaysian impatience with the situation.
In Manila, Philippine President Benigno Aquino also urged the gunmen to surrender immediately.
"To those who have influence and the capacity to reason with [the sultan's followers], I ask you to convey this message: surrender now, without conditions," he said in a statement.
The Filipinos, who are estimated to number between 100 and 300, sailed from their remote islands to press Jamalul Kiram III's claim to Sabah.
Kiram, 74, claims to be the heir to the Islamic sultanate of Sulu, which once controlled parts of the southern Philippines and a portion of Borneo.
In an immediate response to Aquino's appeal, Kiram's spokesman Abraham Idjirani said the gunmen would remain in Sabah.
"We have spoken: It's honour over lives," he said, adding that the deaths of the sultan's followers have "only strengthened our resolve to defend the rights of the Filipino people over Sabah".
Malaysian Prime Minister Najib Razak, whose government has been embarrassed by the security breach, said doors for negotiation are closed and urged the gunmen to surrender.
"The Sulu rebels have to surrender or they will face the action of our security forces," he was quoted as saying by the Star newspaper.
While it is not clear how the firefight erupted, Najib said the two police officers were gunned down after walking into a trap.
"I was told some Sulu gunmen had waved the white flag but when the Malaysian forces moved in, they were fired upon instead," he said.
Muslim-majority Malaysia had previously avoided tough talk, expressing hope the intruders would leave peacefully.
But now, even if they give up, they will face Malaysian prosecution, Hamza said, after he met with Malaysia's home minister and other top security officials.
Local residents were staying indoors and the usually bustling coastal town of Lahad Datu, the area's only major town, about 150km from the standoff site, was quiet with most shops closed on Saturday.
The Sulu sultanate's power faded about a century ago but it has continued to receive nominal payments from Malaysia for Sabah under a historical lease arrangement passed down from European colonial powers.