SULTAN KUDARAT: The Philippines' largest Muslim militant group said Saturday it has potentially serious rebellion in its ranks after a key leader broke away ahead of peace talks with Manila.

Ameril Umbrakato resigned from the Moro Islamic Liberation Front (MILF) seven months ago, taking with him at least a thousand MILF fighters, top MILF leaders told a news conference.

The development poses a potentially major problem to formal peace talks scheduled to start in Malaysia on Wednesday, conceded Murad Ebrahim, chairman of the 12,000-member movement.

"We are talking with them and urging them to toe the line on the MILF position," Murad said.

Previous peace talks collapsed in 2008 after the Supreme Court outlawed a draft peace settlement that would have given the MILF control over large areas of the mineral-rich southern island of Mindanao.

The group has begun waging a rebellion since 1978 for an independent Muslim state on Mindanao, which makes up the southern third of the largely Roman Catholic Philippines.

The Supreme Court's decision triggered attacks by MILF commanders including Umbrakato on Christian communities in Mindanao. The resulting surge in violence displaced 750,000 people and left nearly 400 dead, according to official data.

More than 150,000 people have died since the early 1970s due to the rebellion, according to the government.

Mohagher Iqbal, head of the MILF peace negotiating panel, said Umbrakato accused the leadership of turning its back on the original goal of an independent Muslim nation.

"He said the MILF is a revisionist group," Iqbal said.

"We have sent Ulmas (Muslim elders) to talk to him and we are trying to engage him," Iqbal added.

The MILF itself is a 1978 splinter of the Moro National Liberation Front, which signed a 1996 peace treaty that won the large Muslim minority limited self-rule in four Mindanao provinces.