Malaysia's military Tuesday launched a fierce assault including jet fighters on up to 300 Filipino intruders after a deadly three-week standoff, as their leader vowed they would fight to the death.
However, Malaysia's national police chief said more than nine hours after the attack began that "mopping up" operations had yet to find any dead militants, and expressed fears that at least some of them might have slipped away.
Prime Minister Najib Razak said he had no choice but to unleash the military to try to end Malaysia's biggest security crisis in years after the interlopers refused to surrender and 27 people were killed.
A day after the Philippines called for restraint, Malaysia launched a dawn assault on the estimated 100-300 gunmen, who invaded to claim Malaysian territory on behalf of a former Philippine sultanate.
Fighter jets bombed the standoff village of Tanduo in Sabah state on the northern tip of Borneo island, followed by a ground assault by troops. The area is set amid vast oil-palm plantations.
"The longer this invasion lasts, it is clear to the authorities that the invaders do not intend to leave Sabah," Najib said.
Federal police chief Ismail Omar told reporters in an afternoon press conference near the standoff site that soldiers were mopping up across a wide area of hilly plantation country but had yet to find any dead militants.
"I have instructed my commanders to be on alert because we believe the enemies are still out there," Ismail said.
"We of course hope that they have not escaped," he said, providing few other details. However, he said Malaysian forces had suffered no casualties.
The Islamic intruders' apparent willingness to risk death over a long-dormant territorial dispute has shocked Muslim-majority Malaysia.
Jamalul Kiram III, 74, their self-proclaimed sultan, said Tuesday in Manila that incursion commanders, including his younger brother "and the many patriots who landed voluntarily will fight to the last man protecting their ideals and aspirations".
The group had been holed up in the village since landing by boat last month, highlighting lax Malaysian security and the continuing threat from southern Philippine Islamists.
Witnesses said fighter jets roared overhead early on Tuesday, followed by the thud of loud explosions.
Amid the assault, an AFP reporter at a roadblock 30 kilometres (19 miles) from Tanduo saw military transport helicopters flying toward the village, as army trucks with dozens of soldiers and several ambulances sped toward the scene.
Philippine President Benigno Aquino's spokesman blamed the intruders for the assault.
"We've done everything we could to prevent this, but in the end, Kiram's people chose this path," said the spokesman, Ricky Carandang.
After a lengthy standoff, violence erupted in Tanduo on Friday with a shootout that left 12 of the gunmen and two police officers dead.
Another gunbattle Saturday in the town of Semporna, hours away by road, killed six police and six gunmen, raising fears of a wider guerrilla infiltration.
Another gunman was reportedly beaten to death by Semporna residents.
Even if the Tanduo operation succeeds, the drama may not end there.
Police said at the weekend they were hunting for a group of "foreign" gunmen in yet another town, but have provided no further updates.
Followers of Kiram, the self-proclaimed heir to the sultanate of Sulu, have warned that more militants were poised to land in Sabah.
The sultanate, based in the southern Philippines' Sulu islands, once controlled parts of Borneo including Sabah.
Its power faded about a century ago but its heirs have continued to insist on ownership of resource-rich Sabah and still receive nominal Malaysian payments under a leasing deal originally struck by Western colonial powers.
The exact identities of the gunmen and their numbers have remained a mystery. Malaysia's opposition has criticised authorities for providing inadequate information on the mayhem and being caught flat-footed by the invaders.
Sabah has seen small raids by Islamic militants and criminals coming by boat from the Philippines before, but nothing on the current scale.