Islamist militants have been blamed for a bomb blast in the Philippines today which killed at least five people and wounded dozens more.

The bomb exploded outside the Immaculate Conception cathedral in Cotabato city, 545 miles (880 kilometers) south of Manila, as church-goers celebrated Mass.

A woman selling roast pork was killed on the spot while four others, including a soldier and three-year-old boy, died in a nearby hospital. Among the wounded were five soldiers who were passing the cathedral in an army van when the device, fashioned from a mortar round, exploded said army spokesman Colonel Jonathan Ponce.

"This is the handiwork of the rogue members of the Moro Islamic Liberation Front (MILF)," Colonel Ponce told reporters, referring to the Muslim organisation which has waged a decades long battle for self rule in the southern island of Mindanao.

The improvised explosive was hidden near a row of food stalls selling roasted pig, said regional military commander Major General Cayton..

Witnesses said the bishop celebrating mass had just finished reading the gospel and was about to begin his homily when an explosion was heard.

"The explosion was so loud as if the cathedral was about to collapse," Merly Sandoval, a churchgoer, told a local radio station.

"It was like loud and frightening thunder. People inside the packed cathedral ran towards the altar. Outside, everybody was screaming, there was so much blood on the ground."

Television footage showed four wounded soldiers sitting dazed on the sidewalk and the fifth lying unconscious, face down on the seat of their shrapnel-damaged van.

Two bodies lay sprawled near the sidewalk while a stunned woman limped out of a food stall, blood dripping from her right foot.

Army troops with assault rifles surrounded the cathedral and cordoned off nearby streets, footage showed.

Major General Cayton blamed the 11,500-strong Moro Islamic Liberation Front, which has been targeted by a months long military offensive in nearby Maguindanao province and outlying regions.

"Nobody has the motive, the capability and the track record to carry out this terrorist attack except the lawless MILF group," Cayton told The Associated Press.

Mohaqher Iqbal, a senior leader of the MILF, the largest Muslim rebel group in the mainly Roman Catholic Philippines, denied his group was involved in the attack.

"Who needs a Christian-Muslim conflict?," Iqbal told Reuters in a mobile phone text message.

"There's no religious conflict in the south. We're fighting for our right of self-determination. We're only defending our people and our communities."

For years MILF has waged low level civil war for self-rule in Mindanao, the homeland of minority-Muslims in the predominantly Roman Catholic nation.

However, rogue members of the MILF have been fighting the army since August, when the government ended peace talks with the organisation after the Supreme Court stopped a deal to expand an existing Muslim autonomous region on Mindanao.

The fighting has forced around 350,000 people have been forced to flee their homes and farms and nearly 600 people have been killed, many of them civilians.

Cotabato city has been hit previously by deadly bombings blamed on Muslim rebels and extortion gangs.

A bomb exploded at a city bus terminal in February, wounding two people.

A 2007 bomb blast at another terminal killed a child and wounded 36 people.

A soldier was killed in a bombing at an airport near the city of more than 250,000 people in 2003. The attacks were also blamed on the Muslim rebels.

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