A fourth suspect in the bombing attempt near the United States in Manila is in police custody, Philippine National Police Director General Ronald Dela Rosa said Thursday.

Dela Rosa, in a news briefing in Camp Crame, said the suspect was captured somewhere in Zambales province.

He withheld the person's identity and other details including to protect ongoing operations.

Authorities are looking for one more suspect in foiled attack on the Philippine capital last November 28. The five belong to one cell of the Ansar Al-Khilafah, a terrorist group based in Mindanao which is reportedly linked to the Islamic State.

Police also recovered on Wednesday an improvised explosive device in Bulakan town, Bulacan based on the information from the third suspect, Mohmmad Jumao-as, who was captured Friday last week in Bulakan.

It's one of the two bombs brought by the suspects from Mindanao. The other explosive device placed about 150 meters from the US Embassy was disposed by the police.

The bomb, fashioned out of an 105 millimeter projectile for a howitzer cannon, was recovered at 3:45 pm submerged in mud in Barangay Santa Ana.

Dela Rosa said the bomb, if detonated in a public place, can kill 200 to 300 people and is stronger than the one which exploded at a night market in Davao City last September.

"It has a blast radius of 70 to 80 meters from the seat of the explosion," he said.

The other components recovered are an electric blasting cap, nine volts battery, packaging tape and a handheld radio as detonating device.

Police are investigating if the suspects brought more bombs from Mindanao Emmanuel Tupas/DMS