The disaster killed two and left 134 of its 899 passengers missing.

The possibility of a suicide bombing led to fears about attacks against election candidates and ordinary Filipinos.

'We should start looking at all possible angles that could give them [the terrorists] media exposure, which is what they're after,' Mr Lozada said.

Veteran anti-terrorist police investigator Rodolfo Mendoza said: 'There is already an indication that Muslim extremists have the boldness to carry out a suicide mission.'

Suspected Abu Sayyaf member Arnulfo Alvardo was aboard the ferry and among the missing, coastguard Rear Admiral Arthur Gosingan was quoted as saying.

Meanwhile, Mr Lozada noted that the Tausug tribe of the southern Philippines, from which the Abu Sayyaf drew its members, had a history of conducting suicide missions at the turn of the 20th century.

Mr Lozada represents Bacolod City in central Philippines, where 67 of the missing passengers were bound. In a call to a radio station on Sunday, an Abu Sayyaf spokesman claimed responsibility for the sinking of the ship and named Alvardo as the suicide bomber.

The Radio Mindanao Network, which has often been called by the Abu Sayyaf in the past, said group spokesman Abu Sulaiman claimed the bomb was planted in revenge for alleged incidents of violence in the southern Mindanao area, including the rape of some Muslim women by Philippine troops.

The fire occurred the same day that two alleged Abu Sayyaf members were convicted of kidnapping an American in 2000 and another was arraigned for a separate mass abduction.

The administrator of the Maritime Industry Authority, Oscar Sevilla, said 'as of now, we see sabotage as the strongest angle in the investigation'.

'The passengers were unanimous in saying that they heard a blast' in economy class, located in the middle section of the 10,192-tonne vessel, he added.

But other officials and the military have downplayed Abu Sayyaf claims, saying it may have been a bluff to project strength amid setbacks that have considerably weakened the group.

Army spokesman Lieutenant-Colonel Daniel Lucero said the group's claim of responsibility was just an attempt to 'ride' the extensive media coverage of the ferry disaster.

Transportation and Communications Secretary Leandro Mendoza blamed the sinking on an explosion in the boiler room or on a defective petrol tank, not a terrorist act.

Investigators said it was too early to pinpoint the cause of the disaster because divers had not yet been able to make a full search of the wreckage or get into the cabin where the alleged suicide bomber could have been.