Salamat Hashim, the chairman of the Moro Islamic Liberation Front (MILF) died on July 13 in Butig in the southern province of Lanao Del Sur, said the MILF political affairs chief, Gazali Jaafar.
"Chairman Salamat died of acute ulcer on July 13 and was buried on the same day," he told a church radio station, DXMS, in Cotabato City. "The MILF central committee decided to delay the announcement to inform the relatives officially," he added.
Hashim, 68, is to be succeeded by the MILF's vice-chairman and military chief Murad Ebrahim, who will also lead peace talks with the government, Jaafar said.
"The death of brother Salamat will not stop the MILF from pursuing a peaceful, political and comprehensive agreement with the Philippine government," Jaafar said.
The MILF has been waging an insurgency in the southern Philippines for the last 25 years to create a new Muslim state in the southern third of the largely Roman Catholic Philippines.
Peace negotiations delayed
Salamat (C) is seen with his
soldiers at their mountain hideout
Last month, the two sides agreed to a truce to pave way for the talks, which were suspended earlier this year amid a spate of bombings and attacks blamed by the military on the MILF.
President Gloria Arroyo had accused the MILF of providing sanctuary to terrorists.
But MILF chief Hashim publicly denied links to groups accused of terrorism including the Jemaah Islamiyah, allegedly linked to al-Qaeda, and agreed to the ceasefire.
Arroyo also suspended arrest warrants against Hashim and the other MILF leaders.
It was announced on Monday that the peace talks between the government and the MILF scheduled in Kuala Lumpur had been delayed but did not give any reasons.
Hashim joined the MILF in 1968 after working as a government librarian. The MILF broke away from another separatist group, the Moro National Liberation Front (MNLF), which had opted for limited self rule in the south.
Salamat was born into an influential, religious family in Maguindanao province in the southern island of Mindano.
The migration of large numbers of Christians over decades had made the Muslims a minority in most parts of the south.
Salamat was not part of the armed groups that battled Christians in the south.
In the 1960s he was sent to Egypt where he obtained an Islamic philosophy degree from al-Azhar University, the world's oldest Islamic university, in 1967 and a masters degree two years later.