JAKARTA, Indonesia — A wave of deadly bombings on Sunday and Monday and evidence of more planned have shaken Indonesia just ahead of the holy month of Ramadan, with entire families — including children — carrying out suicide attacks against Christian worshipers and the police.
The troubling discovery Monday of a trove of completed bombs in a housing complex outside Surabaya, Indonesia’s second-largest city, came a day after members of a single family carried out three attacks against separate churches in the city around Mass time, killing seven people.
On Sunday night, three members of another family, including a child, were killed when a bomb exploded at their apartment outside Surabaya when the police moved in to arrest them.
And on Monday morning, a family of five riding on two motorbikes detonated a bomb at the entrance of the Surabaya Police Headquarters — killing all but one of them and injuring four police officers. An 8-year-old girl who was with the attackers survived the blast and was taken to the hospital.
The extent of the carnage and the fact that children were enlisted in the attacks drew condemnation from the country’s leader, President Joko Widodo, who called them “barbaric.” All told, 12 civilians and 13 terrorist suspects were dead from two days of violence, with at least 46 people injured, including police officers.
Police officials said the attackers, whether by blood or other ties, were working together.
“They’re from one organization,” Gen. Tito Karnavian, chief of the National Police, said during a Monday news conference in Surabaya. The city, the capital of East Java Province with a population of almost three million, has a large ethnic Chinese Christian community.
A day earlier, General Karnavian had said the family suspected in those attacks had recently returned to Indonesia after being deported from Syria.
On Monday, General Karnavian said the bombs that exploded on Sunday and Monday were similar in their construction — highly-powerful and sensitive to movement — to those used by the Islamic State in its war in Iraq and Syria.
He said that these types of bombs are known as the Mother of Satan.
The Islamic State has claimed responsibility for the attacks, describing each of the bombings as a “martyrdom” operation carried out by three modes of attack: a car bomb, a suicide vest and a motorcycle-borne bomb.
Indonesia, the world’s most populous Muslim-majority nation, practices one of the most moderate forms of Islam in the world, but still has a homegrown terrorism problem. The country has experienced numerous attacks in the years after the Sept. 11 attacks in the United States, including deadly terrorist bombings on the resort island of Bali in 2002 and 2005, and bombings of international hotels in Jakarta in 2003 and 2009.
But the use of children in terrorist plots, analysts say, represents a new and shocking development in Indonesia.
“It was in one way expected and also completely unexpected, and that raises it to a new level of sick, using kids in this kind of thing,” said Ken Conboy, a security consultant and counterterrorism analyst in Jakarta.
During Sunday morning’s attacks, one suicide bomber appeared to have been disguised as a churchgoer. In another, an attacker drove a Toyota minivan with a bomb the site. Still another attacker was seen in footage speeding on a scooter toward a church before an explosion.
In Sidoarjo, a suburb south of Surabaya, a bomb detonated within a family’s apartment as the police closed in on Sunday night, killing the husband and wife and one of their children, and injuring another three children, said a spokesman for the provincial police, Frans Barung Mangera. He identified the dead suspect as Anton Ferdiantono, 46, who police officials later said was a friend of the man behind the church bombings.
In the final burst of violence, on Monday, four of the five people on the motorcycles were killed, and the fifth, the 8-year-old girl, was taken to the hospital, said Mr. Frans, the police spokesman. Four police officers were reported injured. A video released by an Indonesian news outlet appeared to show the explosion centered on one of the motorcycles, flattening police officers and damaging another car.
The counterterrorism police said they raided another housing complex in Sidoarjo on Monday morning, recovering several completed bombs after having neighboring residents evacuate.
The wave of deadly attacks began with the Sunday church bombings, which left at least 43 people injured and occurred in different parts of the city within minutes of each other, according to the police.
The family members in the church bombings have been identified as Dita Oepriarto and his wife, Puji Kuswati. Two of their sons, ages 18 and 16, were also involved, as well as two daughters, ages 9 and 12, according to the police.
The police said the father had dropped off his wife and two daughters at the Indonesia Christian Church. There, the wife tried to force her way inside, detonating a bomb outside the entrance and killing herself and her two daughters, the police said.
The sons rode motorcycles to their target, the Santa Maria Church, before detonating their explosives, according to the police.
The father was behind the wheel of the vehicle that crashed into the third church, the Surabaya Center Pentecostal, detonating a bomb believed to have been in the vehicle, the police said.
All six of the family members died in the explosions, the police said.
The police later disabled three bombs at the family’s home.
The bombings occurred as professed followers of the Islamic State have begun to make their presence felt in Indonesia, which is proud of its diversity and religious tolerance.
Last Wednesday, the Islamic State said it was responsible for a riot at a police detention center near the Indonesian capital, Jakarta, which housed dozens of terrorist suspects and convicts, most of them members of an Indonesian terrorist network that has sworn allegiance to the Islamic State.
Detainees killed five guards before order was restored, and one detainee was also killed.
In 2016, the Islamic State, also known as ISIS, claimed its first attack in Southeast Asia, when militants attacked a police post and shopping center in central Jakarta, the Indonesian capital, with homemade guns and bombs.
Amir Tejo contributed reporting from Surabaya, Indonesia, Muktita Suhartono from Bandung, Indonesia, Muhammad Rusmadi from Jakarta, and Rukmini Callimachi from New York.