Muslim separatists in the southern Philippines have said they will take their case to the UN and Islamic nations, after the country's Supreme Court threw out a proposed deal granting them greater autonomy.

The court on Tuesday declared unconstitutional the draft accord to grant minority Muslims expanded self-rule in their southern homeland in a bid to end decades of separatist fighting.

Violence in the southern Mindanao region flared up in August, leaving nearly 100 dead and half a million displaced, after Roman Catholic politicians protested against the government's planned signing of the accord.

Some Moro Islamic Liberation Front (MILF) fighters went on a bloody rampage and the government then abandoned the deal, suspended peace talks and launched an offensive to capture three rebel commanders blamed for the attacks.

Mohagher Iqbal, chief negotiator for the MILF, said the only option left for the separatists was to take the accord to the United Nations and the Organisation of the Islamic Conference to seek their guarantees that if talks resume their outcome will be respected.

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Conflict in Mindanao

He criticised the government of Gloria Arroyo, the president, for backing out of the deal after 11 years of negotiations, and warned that militants among the separatists opposed to the peace process may stage fresh attacks.

"After long years, we came to a point that seemed to bolster what the anti-negotiation groups are saying: that the government could not be trusted," Mohagher Iqbal said.

The MILF has been battling for self-rule in the predominantly Roman Catholic nation's volatile south for decades.

Despite the latest setback, both sides said they will respect a 2003 ceasefire, which has been monitored by a handful of international observers.