Four were killed while 45 were injured as an improvised bomb exploded at the 7 am mass at a gymnasium in a university in Marawi on Sunday.

''This happened while there was Sunday mass at Dimaporo Gymnasium,'' said Maj. Alinaid Moner, public information office head of the Lanao del Sur Provincial Police Office, in an interview at dzBB.

Moner said five of the injured are in ''critical condition.''

President Ferdinand Marcos Jr., in a statement, blamed ''foreign terrrorists'' for this bombing. He denounced the incident, adding the government will ''bring the perpetrators of this senseless act to justice.''

Armed Forces chief Gen. Romeo Brawner Jr. said in a press conference the bombing ''may have been a retaliatory attack (of the terrorists).''

On Saturday, the military announced that 11 alleged members of the Daulah-Islamiya, including its leader, were killed in an encounter with security forces.

Asked if the bombing is connected to the Israel-Hamas conflict, Defense Secretary Gilberto Teodoro Jr. said at a press conference: '' We are not at liberty to say.''

Teodoro added that there are '' indicia of foreign element here which we are looking into.''

Teodoro said that the Philippine National Police has gone on heightened alert in the National Capital Region. DMS