MANILA, April 14 (Reuters) - The Philippines' most dangerous Muslim militant group is one of the main suspects in Sunday's twin bomb attacks, one outside a Catholic cathedral, in a southern city, security officials said on Monday.

"The Abu Sayyaf Group is one of our primary suspects," said Jonathan Perez, Zamboanga City police chief, showing reporters a sketch of one of the suspected bombers.

No one was hurt in the pre-dawn blasts in Zamboanga City, where dozens of members of the U.S. special forces are based, but the attacks raised fears of a renewed campaign of violence by Abu Sayyaf.

Perez said the type and make of the explosive devices used in the attack on the cathedral and another blast near a branch of Malaysian bank Maybank <MBBM.KL> were similar to those used by the Abu Sayyaf in previous attacks in other parts of the south.

"The signature on the bombs were almost identical. They used a mobile phone to detonate a crude bomb made from an 81mm and 60mm mortars," he said.

Perez said the suspects were trying to plant the bombs inside the Immaculate Concepcion Metropolitan Cathedral before the first mass on Sunday at 5 a.m., but they were forced to leave them under a pickup truck outside when people noticed them.

"They threw the second bomb about a kilometre away near the MayBank branch when a group of police officers tried to accost them," he added.

The Abu Sayyaf is a small but deadly Muslim militant group operating in the south of the largely Roman Catholic Philippines. It was blamed for the country's worst terrorist attack, the bombing of a ferry near Manila Bay in 2004, which killed more than 100 people.

While mainstream Muslim rebel groups have signed truces with Manila and are negotiating for some measure of self-rule in the south, the Abu Sayyaf continues to bomb and uses kidnap-for-ransom to fund its activities.

Since 2002, Washington has been helping its former colony hunt down members of Abu Sayyaf and Jemaah Islamiah (JI), a regional terrorist network, through training and equipment. (Reporting by Manny Mogato; editing by Carmel Crimmins)

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