FELDA SAHABAT, Malaysia (AFP) ― Malaysia’s military Tuesday launched a fierce assault including jet fighters on up to 300 Filipino intruders after a deadly three-week standoff, but the militants’ supporters said they had escaped and were alive and well.

Malaysia’s national police chief had also raised doubts about the success of the air and ground attack, saying “mopping up” operations had yet to find any bodies and suggesting at least some of the militants might have slipped away.

Malaysian premier Najib Razak said as the raid was under way that he had no choice but to unleash the military 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 on Borneo island, 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 in a statement.

But Abraham Idjirani, spokesman for the sultan Jamalul Kiram III, said the attack had occurred “away from where” their men were, saying he spoke with the leader of the armed group about eight hours after the assault was launched.

Malaysian federal police chief Ismail Omar later told reporters in a press conference hours after the initial attack that soldiers combing across a wide area of hilly plantation country were yet to find any dead militants.

He added Malaysian forces had suffered no casualties.

If the invaders had indeed escaped a tight police and military cordon, it would likely fuel perceptions of incompetence by security forces in the affair, and sow fears that armed and dangerous gunmen were loose.

The crisis comes as Malaysia’s 56-year-old ruling coalition is bracing for what are widely expected to be the country’s closest-ever election against a formidable opposition, which has criticized handling of the incursion.

Jamalul Kiram III, 74, a self-proclaimed sultan and leader of the insurgents said earlier Tuesday in Manila that the fighters, which had included his younger brother “will fight to the last man.”

Muslim-majority Malaysia has been shocked by the spectacularly bold attack by the Islamists, who claim to be asserting Jamalul’s ancestral control of Sabah as heir to the now defunct Sulu sultanate.

The invaders had been holed up in Tanduo village since landing by boat last month, highlighting lax Malaysian security in the region and the continuing threat from southern Philippine Islamists.

“We’ve done everything we could to prevent this, but in the end, Kiram’s people chose this path,” a spokesman for Philippine President Benigno Aquino said.

Violence first 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.

Police had already said at the weekend they were hunting for a group of “foreign” gunmen in yet another town, but have provided no further updates.

Meanwhile, followers of Kiram, have repeatedly warned that yet more militants were poised to land in Sabah.

Members of a major Philippine Muslim rebel group, the Moro National Liberation Front who had agreed to disarm in the 1990s and renounce its claim over Sabah as part of a peace pact, are also involved in deadly battles in Malaysia, the group’s leader said.

The Philippines also said that its navy had stopped 70 more people from getting across the sea border to help the militants.

The mayhem triggered panic in Semporna, where many residents were witnessed by an AFP reporter fleeing the town on Monday, fearing more violence.

The Sulu sultanate’s power faded about a century ago but its heirs continue to insist on ownership of resource-rich Sabah and still receive nominal Malaysian payments under a lease deal originally struck by Western colonial powers.