An influential leader of the Philippines' decades-long Muslim separatist insurgency voiced support Thursday for peace efforts after rebellion charges against him were suspended and he held a surprise meeting with President Rodrigo Duterte.

Moro National Liberation Front founder Nur Misuari was flown on a government-commissioned plane more than 900 kilometres (550 miles) from his southern jungle stronghold to Manila for the meeting with Duterte at the presidential palace.

"I came here to thank him for restoring my freedom, if only partially," Misuari said.

"Should he need our cooperation in his campaign for peace, you can count on us."

Misuari, 77, had been in hiding since his forces allegedly launched attacks on civilians in the southern city of Zamboanga in 2013, leading to a three-week battle against the military that claimed about 200 lives.

The government of Duterte's predecessor, Benigno Aquino, filed rebellion charges against Misuari, but he was able to remain on his southern island stronghold of Jolo under the protection of his armed followers.

Misuari, a charismatic scholar, founded the MNLF in 1972 to wage a guerrilla war for a separate Islamic state in the south of mainly Catholic Philippines. Most of the nation's Muslim minority live in the southern region of Mindanao.

The conflict, which also involved other rebel groups, is believed to have claimed more than 120,000 lives and contributed to Mindanao remaining the nation's poorest region.

Misuari signed a peace agreement with the government in 1996 in return for the creation of a Muslim autonomous area of which he became governor.

However the conflict persisted as the Moro Islamic Liberation Front, a splinter organisation with more than 10,000 armed followers, continued the rebellion. The MILF in recent years also began negotiating for peace.

Misuari allegedly orchestrated the 2013 Zamboanga attacks because he felt the MNLF was being sidelined under the planned MILF peace deal with Aquino.

Duterte is aiming to forge a final peace agreement with both groups, although he has not announced concrete plans on how he would do that or settle their rivalries.

It also remains unclear how many armed followers Misuari still has, and how much control he continues to hold over the MNLF.

Misuari on Thursday insisted he remained a powerful force, and that thousands of men from other rebel groups had switched to become his followers.

"Most of the fighters are already with me," he said.

Duterte told reporters he had personally ordered the rebellion charges against Misuari to be "lifted".

However a court document showed the arrest warrant against Misuari had only been "suspended" for six months.