MAKASSAR, Indonesia (AP) — Two attackers believed to be members of a militant network that pledged allegiance to the Islamic State group blew themselves up outside a packed Roman Catholic cathedral during a Palm Sunday Mass on Indonesia’s Sulawesi island, wounding at least 20 people, police said.

Rev. Wilhelmus Tulak, a priest at the Sacred Heart of Jesus Cathedral in Makassar, said he had just finished celebrating Palm Sunday Mass when a loud bang shocked his congregation. He said the blast went off at about 10:30 a.m. as a first batch of churchgoers was walking out of the church and another group was coming in.

He said security guards at the church were suspicious of two men on a motorcycle who wanted to enter the building and when they went to confront them, one of the men detonated his explosives.

Police later said both attackers were killed instantly and evidence collected at the scene indicated one of the two was a woman. The wounded included four guards and several churchgoers, police said.

National Police Chief Gen. Listyo Sigit Prabowo told reporters when he visited the crime scene late Sunday that the two attackers are believed to have been members of the militant group Jemaah Anshorut Daulah, which has pledged allegiance to Islamic State group and was responsible for deadly suicide bombings on Indonesian churches in 2018.

He said one of the attackers was believed to have links to a church bombing in the Philippines.

The attack a week before Easter in the world’s most populous Muslim-majority nation came as the country was on high alert following December’s arrest of the leader of the Southeast Asian militant group, Jemaah Islamiyah, which has been designated a terror group by many nations.

Indonesia has been battling militants since bombings on the resort island of Bali in 2002 killed 202 people, mostly foreign tourists. Attacks aimed at foreigners have been largely replaced in recent years by smaller, less deadly strikes targeting the government, police and anti-terrorism forces and people militants consider as infidels.

Police have identified one of Sunday’s attackers only by his initial, L, who they believe was connected to a 2019 suicide attack that killed 23 people at Our Lady of Mount Carmel Cathedral in the Philippine province of Sulu, Prabowo said.

He said the two attackers were linked to a group of suspected militants arrested in Makassar on Jan. 6, when a police counterterrorism squad shot and killed two suspected militants and arrested 19 others. Members of the squad were initially supposed to arrest the two slain men for their alleged role in the Philippine suicide bombing.

He said on Sunday police arrested four suspected militants believed to have links with the attackers in a raid in Bima, a city on Sumbawa island in East Nusa Tenggara province.

“We are still searching other members of the group and I have ordered the Densus 88 to pursue their movement,” Prabowo said, referring to Indonesia’s elite police counterterrorism squad.

Indonesia’s last major attack was in May 2018, when two families carried out a series of suicide bombings on churches in the city of Surabaya, killing a dozen people including two young girls whose parents had involved them in one of the attacks. Police said the father was the leader of a local affiliate of Jemaah Anshorut Daulah.

President Joko Widodo condemned Sunday’s attack and said it has nothing to do with any religion as all religions would not tolerate any kind of terrorism.

“I call on people to remain calm while worshipping because the state guarantees you can worship without fear,” Widodo said in a televised address.

He offered his prayers to those injured and said the government would cover all costs of medical treatment. He said he had ordered the national police chief to crack down on any militant network that may be involved.

At the end of Palm Sunday Mass in St. Peter’s Basilica, which opened Holy Week ceremonies at the Vatican, Pope Francis invited prayers for the victims of violence. He cited in particular “those of the attack that took place this morning in Indonesia, in front of the Cathedral of Makassar.”

“We join with Pope Francis in praying for the victims of this horrendous attack,” said a statement emailed to The Associated Press by the Archdiocese of Washington.

In Atlanta, where the archdiocese is home to many Asian communities, Archbishop Gregory J. Hartmayer said in a statement that “As we enter today into the holiest week of the year, we grieve once again for the victims of senseless violence. I join in prayer for those killed and injured in the suicide bombing in Indonesia.”

A video of the scene of the attack obtained by The Associated Press showed body parts scattered near a burning motorbike at the gates of the church.

At least 20 people were wounded in the attack and had been admitted to hospitals for treatment, said Mohammad Mahfud, the coordinating minister for political, legal and security affairs.

Indonesia has been on high alert since police in December arrested Jemaah Islamiyah leader Aris Sumarsono, also known as Zulkarnaen. Over the past month the country’s counterterrorism squad has arrested about 64 suspects, including 19 in Makassar, following a tipoff about possible attacks against police and places of worship.

Jemaah Islamiyah was once considered the preeminent terror network in Southeast Asia, but has been weakened over the past decade by a sustained crackdown. In recent years, however, a new threat has emerged in militants who fought with the Islamic State group in Iraq and Syria and returned to Indonesia or those inspired by the group’s attacks abroad.

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Karmini reported from Jakarta, Indonesia.