The suicide bombing at an Indonesian cathedral on Palm Sunday was carried out by two members of a pro-Islamic State extremist group blamed for other church blasts, including a deadly 2019 attack in the Philippines, police said.

About 20 worshippers were injured by the powerful explosion outside the church in Makassar city on Sulawesi island as they celebrated the start of Holy Week.

Both suspects in the attack were killed as they rode a motorbike into the compound of the church, setting off what authorities said was an improvised explosive device known as a pressure-cooker bomb.

A church security guard tried to prevent the two perpetrators from entering when the blast occurred, they added.

Late Sunday, National Police chief Listyo Sigit Prabowo said both attackers -- a man and a woman -- were members of Jamaah Ansharut Daulah (JAD), an extremist group also blamed for a deadly church bombing in Indonesia's second-biggest city Surabaya in 2018.

Indonesia terror attack
The powerful blast hit a church in Makassar city on Sulawesi island Photo: AFP / DAENG MANSUR

Prabowo did not give names or say how they were identified, but forensic examiners were performing DNA tests on body parts scattered at the grisly scene.

"There were two perpetrators killed, one is a man and another one is a woman," Prabowo said.

"They're members of the JAD group which carried out a bomb attack in Jolo in the Philippines."

It was not clear if the pair were a married couple.

An Indonesian militant and his wife -- members of JAD -- were blamed for two explosions that ripped through a Catholic church on the Philippines' Muslim-majority island of Jolo in 2019, killing worshippers at Sunday mass and security forces.

Indonesia terror attack
Police said a church security guard tried to prevent the motorbike from entering the compound when the blast occurred Photo: AFP / INDRA ABRIYANTO

Two other militants linked to that attack were shot dead by Indonesian security forces earlier this year.

One witness to Sunday's bombing described hearing two "very strong" blasts and then seeing plumes of smoke, an attack that wounded about 20 church officials, congregants and security staff.

"There were several injured people on the street. I helped one woman... who was wounded and covered in blood," Yosi, who like many Indonesians goes by one name, told AFP.

"Her grandchild was also injured. There were body parts everywhere."

Indonesia terror attack
Churches have been targeted in the past by extremists in Indonesia, the world's biggest Muslim-majority nation Photo: AFP / INDRA ABRIYANTO

Indonesian President Joko Widodo said he "strongly condemned this act of terror".

"Terrorism is a crime against humanity," he said.

"I call on everyone to fight against terror and radicalism, which go against religious values."

Amnesty International said the bombing showed "complete contempt" for human rights.

The explosion at the main Catholic cathedral in Makassar -- a port city of about 1.5 million -- happened just after congregants finished celebrating Palm Sunday, the first day of Holy Week, which commemorates Jesus's entry into Jerusalem.

It comes a week before Easter.

In his mass for Palm Sunday, Pope Francis said he prayed for all the victims of violence, "especially those of this morning's attack in Indonesia, in front of the Cathedral of Makassar".

Sunday's attack follows the arrest in recent months of dozens of militants suspected of planning terror attacks.

Indonesia has seen a string of attacks by Islamic extremists over the past two decades, including the 2002 Bali bombings which killed more than 200 people, mostly foreign tourists.

The bombings were Indonesia's deadliest terror attack.

In 2018, a dozen people were killed when a family of suicide bombers driving motorbikes blew themselves up at churches during Sunday services in Indonesia's second-biggest city Surabaya.

The family -- including two daughters aged nine and 12 -- and another family of five, which carried out a suicide bombing on a police headquarters, all belonged to the same Koran study group.

They were also linked to JAD, which has pledged allegiance to Islamic State.

JAD first gained notoriety in 2016 for a gun and suicide bomb attack in the capital Jakarta that killed four civilians and four attackers -- including one who blew himself up at a Starbucks outlet.

It was the first attack claimed by Islamic State in Southeast Asia.

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