COTABATO, PHILIPPINES - Foreign Islamic militants may have had a link to a bombing outside a church in the southern Philippines that killed five people and injured dozens, a military spokesman said Monday.

Major Randolph Cabangbang said investigators were probing whether Jemaah Islamiyah (JI), the group behind the Bali bombings, may have been involved in the blast outside the Immaculate Conception Roman Catholic cathedral.

He told reporters a number of JI militants are "here in the country."

Known members of the group Dulmatin, Umar Patek, and Zulkifli bin Hir are thought to be operating in the southern Philippines, he said, but added that there was no proof as yet they were involved.

"There's an ongoing operation to capture those terrorists. We have a directive from Manila to augment our bomb experts and to provide additional bomb-sniffing dogs," he added.

The Philippine military believe JI militants in the Philippines have given bomb-making training to another Islamic separatist group, the Moro Islamic Liberation Front (MILF). The military alleges the MILF is behind some previous bombings of Christian targets in the southern Philippines.

But the MILF denied any involvement in Sunday's bombing. "We are not responsible for the bombing," MILF spokesman Eid Kabalu told reporters.

"We even condemn this attack."

US military advisers are helping with the investigation, Cabangbang added. Small numbers of US military advisers are deployed in the southern Philippines to train Filipino troops fighting Islamic militants in a region wracked by decades of Muslim separatist rebellion.

"US forces are helping their counterparts by providing support. They have their own bomb experts and they would share analysis with each other," Cabangbang told reporters.

"(The Americans) are not directly involved in the hunt against the bombers. They would analyse if foreign terrorists have (a) hand in the attack."

Meanwhile, another military spokesman, Lieutenant-Colonel Jonathan Ponce, said one man was being questioned by police after being picked up by military agents in the city immediately following the blast.

"The suspect was trapped because he's not familiar (with) the city," Ponce said.