Rogue Muslim rebel leader Ameril Umbrakato, whose forces have threatened the peace efforts of the government, has fallen ill, a spokesman for his group said on Saturday.

However the 65-year-old is not dead despite a flurry of reports of his demise, said Abu Misri Mama, spokesman of the Bangsamoro Islamic Freedom Fighters faction, in the strife-torn southern island of Mindanao.

"Four days ago, (Umbrakato) was walking around the camp when his vision darkened and he collapsed," Mama told AFP.

"He regained consciousness three minutes later and told his followers they should go back because he did not feel well."

Mama said that a vice-commander had taken Umbrakato to a doctor and he had not been seen since. The vice-commander said he was merely suffering from asthma.

But sources in the rebel group said that Umbrakato could barely speak anymore and was communicating through writing.

Mama said that if the rebel leader died, they would announce it publicly.

The local army commander, Major General Rey Ardo, said he had also heard reports of Umbrakato's death or that he had suffered a stroke, but was trying to verify them.

He reiterated an earlier offer to have Umbrakato treated at a military hospital.

Von Al-Haq, spokesman of the main Muslim rebel group, the Moro Islamic Liberation Front (MILF), said he had also heard the reports of Umbrakato's death but could not confirm them.

Umbrakato and his group began distancing themselves from the MILF after the main organisation opened peace talks with the government to negotiate an end to the 33-year Islamist insurgency in the south of the Philippines.

Umbrakato, who is believed to have as many as a 1,000 followers, rejected the talks and accused his former comrades of abandoning the fight for an independent Muslim homeland in Mindanao.

He was one of two hard-line MILF leaders who led large-scale attacks across Mindanao in August 2008 after the Supreme Court outlawed a draft peace deal that would have given the MILF control over vast areas of the south.

About 400 people died and 750,000 were displaced in that attack.

In recent months, members of Umbrakato's "freedom fighters" have clashed with MILF members over land disputes.