Police in the Philippines are chasing four men, including two linked to a local militant group, in connection with the deadly bombing of a Catholic mass in the restive south, authorities said Tuesday.

A manhunt was underway after Sunday's attack on worshippers inside a university gymnasium in Marawi, the country's largest Muslim city, which was besieged by Islamist militants in 2017.

Four people were killed and 50 were wounded in the bombing that was later claimed by the Islamic State group. 

President Ferdinand Marcos blamed "foreign terrorists" for the assault.

Police have identified two Filipino men — both with criminal records that include murder — who were seen by witnesses inside the gym before the blast.  

"Their actions were very suspicious. That led to the suspicion that they might be involved in the explosion," spokeswoman Colonel Jean Fajardo told reporters.

"There's an ongoing pursuit operation," she said.  

Police had not yet identified the other two men or a motive for the attack. 

Fajardo said the two Filipino suspects belonged to a militant group "previously involved in bombing incidents in Mindanao", but she declined to release its name.

Army chief General Romeo Brawner said previously that the attack may have been revenge for recent military operations against three militant groups — Dawlah Islamiyah-Philippines, Abu Sayyaf and Maute.

One of those operations killed an Abu Sayyaf "bomb expert", who was allegedly responsible for the 2019 deadly attack on a cathedral on the southern island of Jolo, Brawner told CNN Philippines on Tuesday.

Pro-Islamic State Maute and Abu Sayyaf militants — including foreign and local fighters — held Marawi under siege in 2017.

The Philippine military wrested back the ruined city after a five-month battle that claimed more than 1,000 lives.

Brawner denied there was an intelligence failure ahead of Sunday's bombing, insisting there should have been "more security measures in place" after the military warned local security forces, government officials and the public of possible retaliatory attacks.

Militant attacks on buses, Catholic churches and public markets have been a feature of decades-long unrest in the region.

Manila signed a peace pact with the nation's largest rebel group, the Moro Islamic Liberation Front, in 2014, ending their deadly armed rebellion.

But smaller bands of Muslim fighters opposed to the peace deal remain, including militants professing allegiance to the Islamic State group. Communist rebels also operate in the region.