At least 20 people have been injured after a suicide bomb attack on a church in Indonesia on Palm Sunday.

The attack happened at the Roman Catholic Sacred Heart of Jesus Cathedral in Makassar, on Sulawesi, at about 10:30 local time (03:30 GMT). 

The cathedral was targeted as people were leaving a service for Palm Sunday, which commemorates Jesus' entry into Jerusalem before his crucifixion and marks the start of Holy Week. 

The BBC reports that two attackers approached the church on motorbikes and that the explosion happened as they tried to enter the compound. 

They were the only fatality in the attack which has been blamed on extremists, although no particular group has claimed responsibility yet. 

Indonesian president Joko Widodo has strongly condemned the attack. 

In a video broadcast, he called it an "act of terrorism", and said the government would ensure everyone can worship freely and "without fear" in the world's largest Muslim-majority country, Reuters reports.

Religious Affairs Minister Yaqut Cholil Qoumas has ordered that security be stepped up around places of worship.

"Whatever the motive is, this attack cannot be justified by any religion because it only does harm to other people," he said.

It is not the first time churches have been targeted in Indonesia. In 2018, at least 13 people were killed and 40 injured in suicide bomb attacks on three churches in Indonesia's second-largest city of Surabaya. 

The attacks were carried out by a family of six, including two daughters aged 12 and 9, who were reportedly Islamic State sympathisizers and had recently returned from Syria. 

In 2000, attacks on churches at Christmas killed about 20 people.