Updated

The Philippine House of Representatives failed on Monday to ratify as expected an autonomy deal that many hope will peacefully settle one of Asia's longest-raging Muslim separatist rebellions and help prevent a repeat of a disastrous Islamic State group-linked siege in the south last year.

The Senate unanimously ratified the bill that aims to establish the new Bangsamoro autonomous region but House members adjourned early amid a reported leadership challenge without approving the autonomy deal. The government negotiated the pact for more than two decades with the largest Muslim rebel group in the country.

Confusion over the House leadership row erupted a few hours before President Rodrigo Duterte was to deliver his annual state of the nation address before a joint session of Congress. Duterte was expected to sign the autonomy bill into law as early as Monday and highlight it in his speech, an early legacy of his presidency, which has come under heavy criticism over his bloody anti-drug crackdown and human rights record.

Thousands of protesters rallied outside the House, where Duterte was to speak.

"We find it unfortunate that the Bangsamoro Organic Law was not ratified before the adjournment of today's session," presidential spokesman Harry Roque said. "We consider this as a temporary setback."

There was no immediate reaction from the Muslim rebels over the latest hiccup to hamper the Malaysian-brokered peace deal, which seeks to replace a poverty- and conflict-wracked autonomous region with a potentially larger, better-funded and more powerful region for minority Muslims in the south of the largely Roman Catholic nation.

In 2008, a planned signing of a preliminary pact was scuttled when opponents went to the Supreme Court, which declared the agreement unconstitutional. New fighting erupted when three rebel commanders attacked Christian communities, leaving more than 100 people dead and about 750,000 villagers displaced before a cease-fire ended the violence.

Presidential adviser Jesus Dureza said House legislators had no issue with the autonomy bill but it got accidentally embroiled in a House leadership row, adding he expected the legislation to be fully ratified at some point. Some House members were pressing Monday to have the bill ratified soon.

The proposed deal marks the latest significant attempt by the Philippine government to negotiate an end to nearly half a century of on and off Muslim uprising that has left more than 120,000 people dead and displaced about 2 million others.

The two largest Moro rebel groups in the south have dropped a demand for a separate Muslim state in exchange for Muslim autonomy and renounced terrorism.

Western governments, however, have been worried over the presence of small numbers of Islamic State group-linked militants from the Middle East and Southeast Asia seeking combat training and collaboration with Filipino insurgents.

Last year, heavily armed Filipino insurgents who have sworn allegiance to the Islamic State group, along with dozens of foreign fighters, laid siege on the southern Islamic city of Marawi. Troops, backed by U.S. and Australian surveillance aircraft, routed the militants after five months of airstrikes and ground assaults that left more than 1,200 mostly Islamic fighters dead and the mosque-studded city in ruins.

Proponents say if the proposed autonomy deal succeeds, fighters of the 11,000-strong Moro Islamic Liberation Front would be absorbed in a regional police force and use their familiarity with the marshy and mountainous hinterlands in the south to fight the extremists and help prevent the region from becoming a breeding ground of terrorism.