A family of six jihadists blew themselves up at three different Christian churches in Indonesia Sunday, killing at least 13 and injuring scores more.

The mother and two young daughters blew themselves up at one church, the father bombed another, and their two sons bombed a third, all in Surabaya, the capital of East Java province. Throughout the world, Christians were celebrating the feast of the Ascension Sunday, commemorating Jesus’ return to the Father 40 days after Easter.

The Islamic State terror group has claimed responsibility for the attacks, and national police chief Tito Karnavian confirmed that the family belonged to an ISIS-inspired network, Jemaah Ansharut Daulah (JAD). This was the deadliest ever ISIS-related attack in Indonesia, since the group began undertaking terror attacks in the country in 2016.

The father, identified by police as Dita Oepriarto, head of a local JAD cell, dropped off his wife, Puji Kuswati, and their two daughters, aged 9 and 12, at Diponegoro Indonesian Christian Church, where they detonated the explosives they had strapped to themselves.

Police said that Oepriarto then drove off, introducing his own explosive-laden car into the grounds of Surabaya Centre Pentecostal Church, where he detonated the bombs.

The two sons, aged 16 and 18, rode motorcycles into Santa Maria Catholic Church, and set off explosives they were carrying.

The three coordinated attacks came at five-minute intervals, beginning with the attack on the Catholic church around 7:30am local time.

Police said that the family were among the hundreds of Indonesians who had journeyed to Syria, where the Islamic State has been combating government forces.

Visiting the scene of one of the attacks, Indonesian President Joko Widodo called the assaults “barbaric,” and said he had ordered police to “look into and break up networks of perpetrators.”

The U.S. Embassy in Jakarta condemned the atrocities in a statement.

“These attacks on peaceful worshipers are an affront to the tolerance and diversity embraced by Indonesians,” it said. “The United States stands with the people of Indonesia, and we offer our deepest condolences to the families of the victims.”

With a population of more than 260 million people, Indonesia is the world’s largest Muslim-majority country. Some 87 percent of the people are Muslim, with Christians making up just 10 percent of the population.

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