MANILA - Foreign nationals visiting the Philippines will face stricter inspection in airports and other gateways to prevent the possible entry of extremists after deadly bomb attacks in the south, the Bureau of Immigration said Thursday.

Authorities cannot discount the possibility that foreign terrorists will attempt to enter the country following the 2 explosions that rocked a cathedral in Jolo, Sulu on Sunday, which left 21 dead and some 100 injured, said bureau spokesperson Dana Sandoval.

"Expected po natin na sa papasok po na mga foreigners, more questions, mas maigting po ang pagbabantay natin," immigration bureau spokesperson Dana Sandoval told radio DZMM.

(We expect that for arriving foreigners, there would be more questions, our monitoring will be more intense.)

The Islamic State militant group has claimed responsibility for the blast, saying 2 suicide bombers donated a belt of explosives.

Tighter checks for foreigners will not inconvenience travelers because a standard assessment in immigration counters should only take some 45 seconds, said Sandoval. Persons of interest will be escorted away from the main queue for secondary inspection, she said.

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The military said it was not discounting the suicide bombing angle and the Islamic State's claim of responsibility, but added that the Abu Sayyaf subgroup Ajang-Ajang was a suspect.

On Wednesday, a grenade blast struck a mosque in Zamboanga City, killing 2 people and injuring 4 others, most of whom were Muslim preachers. Police have not determined the motive for the attack but said it was gathering evidence against 2 persons of interest.

There was no link so far between the mosque and cathedral blasts, Defense Secretary Delfin Lorenzana said Wednesday.

The attacks came despite Duterte placing the whole Mindanao under martial law since May 2017 after Maute terrorists laid siege to the southern city of Marawi, unfurling flags of the IS, to whom they pledged allegiance.