Negotiations with the Moro Islamic Liberation Front (MILF) are set to resume in Kuala Lumpur on Wednesday, more than seven months after President Benigno Aquino promised to pursue peace talks to end an insurgency that began in the late 1960s.

At the weekend, the MILF said a senior field commander, Ustadz Ameril Umbra Kato, had broken away and formed a new group to continue fighting to set up an independent and separate Muslim state in the south.

The 11,000-member MILF, which wants self-rule in the south of the mainly Roman Catholic state, is itself a breakaway from separatists who reached a deal with an earlier government, so the new splinter group raises questions about the peace talks.

“The separate existence of another armed group... may significantly put in question the ability of the current leadership of the MILF to deliver on any commitment that is negotiated with the government,” Marvic Leonen, the government’s chief peace negotiator, told reporters on Monday.

“The government panel is, of course, seriously concerned with this development,” he said, saying clarification from the MILF would be sought at this week’s talks.

The conflict, one of two long-running insurgencies that have hobbled development and investment in the Southeast Asian nation, has killed 120,000 people, displaced 2 million and stunted growth in the poor but resource rich area.

Kato was a key figure behind an outbreak of violence in August 2008 after a deal creating an ancestral homeland for Muslims was nullified by the Supreme Court. He led attacks on Catholic-dominated villages in the central region of Mindanao, displacing more than 750,000 people at the height of the conflict.

Last December, a video circulated in the south announcing the creation of a small breakaway MILF faction called Bangsamoro Islamic Freedom Fighters (BIFF) led by Kato.

Mohagher Iqbal, the rebels’ chief negotiator, said they have held talks with Kato to try to convince him to disband his group and support peace negotiations, which he described as the “most viable and practical solution” to end the rebellion.

“We cannot allow two armed groups to operate under the MILF,” Iqbal told Reuters before he boarded a flight to Kuala Lumpur on Monday. “He has to toe the line. We’re close to sealing a deal with the government.”