"So far, no Indonesians have fallen victim. The [Indonesian Embassy in Manila] continues to monitor [the situation] and coordinate with local authorities on the issue," Indonesian Ambassador to the Philippines Sinyo Harry Sarundajang told The Jakarta Post on Sunday night.

Sinyo said the embassy had conveyed Indonesia’s deepest condolences to the victims' families and condemned the attack.

On Monday morning, the Foreign Ministry decried the attack through its Twitter account:

"Our deepest condolences to the government of the Philippines and families of the victims. We wish a speedy recovery for the wounded," the message read.

At least 20 people were killed, including soldiers rushing to aid the wounded, as two bombs hit a church on a southern Philippines island that is a stronghold of Islamist militants, just days after a regional vote for a new autonomous Muslim region.

The first blast occurred inside the Catholic church on war-torn Jolo on Sunday morning, as mass was being celebrated, and was followed by a second explosion in the parking lot as troops responded, regional military spokesman Lt. Col. Gerry Besana told AFP.

At least 77 people were reportedly wounded.

"The motive is surely [...] terrorism. These are people who do not want peace," Besana said.

President Rodrogo Duterte vowed to crush the terrorists.

“The enemies of the state have boldly challenged the capability of the government to secure the safety of the citizenry in that region,” Duterte spokesman Salvador Panelo said as quoted by Reuters.

The armed forces of the Philippines will rise to the challenge and crush these godless criminals.”

Philippines police suspected that the militant group Abu Sayyaf was responsible for the bombings. The group has pledged allegiance to the Islamic State group.

“They want to show force and sow chaos,” National Police chief Oscar Albayalde told DZMM radio, as quoted by Reuters, suggesting the Abu Sayyaf group was the prime suspect. (evi)