MANILA, PHILIPPINES - Islamist militants continue to pose a serious terrorist threat in the Philippines despite a series of high-profile arrests of alleged bomb-makers, the military said Friday.

The crackdown has crippled cells devoted to making and planting improvised explosive devices, including roadside bombs similar to those in use in Afghanistan and Iraq, said the top military commander for the Manila area, Major General Reynaldo Mapagu.

However, he cautioned: 'As long as there are groups or there are people who have ill motives, terrorism will always be a threat to all of us.'

The latest known government operation on Wednesday led to the arrest of three men whom Mapagu described as 'principal participants' in a group allegedly led by Abdul Basit Usman, one of the country's most wanted men.

Usman had sent the three to Manila to prepare bombings in the area, the military said in a statement.

Pakistani intelligence services suggested earlier this year that a man of the same name had been killed in a US drone attack near Pakistan's border with Afghanistan but Mapagu said it was not the same person.

Usman, said by the military to be connected to foreign terrorist groups Jemaah Islamiyah and the Abu Sayyaf, has a compact circle of bomb-makers numbering 'in the vicinity of double digits,' Mapagu told a news conference.

However following the latest arrests, he added: 'The number that they have is down to close to single digits.' The three were arrested in a southern Manila slum populated by tens of thousands of Muslim migrants.

However, Mapagu said Jemaah Islamiyah members thought to be hiding in the southern Philippines to evade prosecution for the 2002 Bali bombings in Indonesia, as well as the 400-strong Abu Sayyaf, had their own people designing and manufacturing bombs.

Western intelligence agencies say these groups, which are also thought to have ties with Al-Qaeda, want to create a pan-Southeast Asian Islamic caliphate encompassing Indonesia, Malaysia, Singapore, and the Mindanao region of the southern Philippines.