Philippine Muslim rebels said Friday they acted purely in "self-defense" in a clash that killed 44 police commandos in the volatile south last month, despite police claims that they were ambushed.

January's botched anti-terror operation in Maguindanao province saw the single biggest loss of life of government forces in recent memory and has cast doubt over the peace process, sparking calls for the resignation of President Benigno Aquino.

The commandos were hunting for one of the world's most wanted terrorists, Bali bomber and Jemaah Islamiyah militant Zulkifli bin Hir, who initial DNA tests show was killed during the fighting.

While authorities claim police came under ambush by the Moro Islamic Liberation Front (MILF) -- who occupy the area where Zulkifli is believed to have been hiding -- the MILF vice chairman gave a different version of events.

"They (rebels) did not ambush the PNP-SAF (commandos)," Ghazali Jaafar told local broadcaster ANC, adding the unannounced police presence gave the rebels the impression that they were under attack.

"The combatants did it in self-defence.... On that basis, they did no wrong," he said.

Civilians who were awakened from their sleep also joined in the fighting, thinking they too were under attack, Jaafar said.

"When a stranger enters your house, and you think your life is in danger, you have to defend yourself," he added.

Eighteen rebels were also killed during the chaotic 12-hour gun battle.

A finger that police cut from what was believed to be Zulkifli's body was sent to the FBI where a preliminary DNA test showed a "possible relationship" with one of the militant's relatives.

The US had offered a $5-million bounty for Zulkifli, a Malaysian bomb-maker who had been hiding in the southern Philippines for over a decade.

Jaafar said the MILF were still conducting an internal probe into the incident.

The Philippine police, military, human rights commission and justice department are also carrying out their own investigations.

In the wake of the incident parliament temporarily suspended hearings on a law that will implement the peace treaty, which will give the country's Muslim minority self-rule in the south.

The landmark peace deal, seen as a major legacy of Aquino, aims to end a decades-old rebellion that has claimed more than 120,000 lives.