MANILA, Dec 8 (Reuters) - The Southeast Asian bloc ASEAN on Friday strongly condemned what it called a "heinous terrorist attack" in the southern Philippines at the weekend in which four people were killed in a bombing at a Catholic Mass.

The bomb went off on Sunday during a service at a university gymnasium in Marawi, a city left in ruins in 2017 by a five-month military campaign to end an occupation by Islamic State loyalists that triggered alarm in Asia about the group's influence.

"We extend our deepest condolences to the bereaved families," the Association of Southeast Asian Nations said in a statement.

Islamic State militants claimed responsibility for Sunday's attack. President Ferdinand Marcos Jr said "foreign terrorists" were behind it and police said they were investigating the incident and validating the claim by the Islamic State group.

Police had identified as suspects two members of Daulah-Islamiyah Maute, a local group involved in the 2017 seizure of Marawi alongside fighters from Indonesia, Malaysia and beyond.

The Philippine military on Friday announced the Dec. 6 arrest in Marawi of a man suspected of placing the bomb in the gymnasium having been being identified by witnesses.

(Reporting by Neil Jerome Morales; Writing by Martin Petty)