Suicide bombings killed at least 11 people and injured over 40 others at three churches in Surabaya, Indonesia's East Java province during Sunday mass. Suicide bombers on motorcycles, including a woman with children, targeted Sunday Mass congregations.
The Islamic State group took responsibility of the attacks via its propaganda agency Amaq.
'Three martyrdom attacks killed 11 and wounded at least 41 among church guards and Christians,' it said via the Telegram messaging app.
A family of six, including two young girls, were responsible for the attacks, national police chief Tito Karnavian said.
The family -- a mother and father, two daughters aged 9 and 12, and two sons aged 16 and 18 -- were linked to local extremist network Jamaah Ansharut Daulah, which supports IS, Karnavian said.
The first attack struck the Santa Maria Roman Catholic Church in Surabaya, killing four people, including one or more bombers, police spokesman Frans Barung Mangera told reporters at the spot.
The blast was followed by a second explosion minutes later at the Christian Church of Diponegoro and a third at the city's Pantekosta Church, Mangera said.
President Joko Widodo arrived in Surabaya, the East Java provincial capital, in the aftermath of the attacks, Mangera said.
The bombings were the worst since a series of attacks on churches on Christmas Eve in 2000 killed 15 people and wounded nearly 100.
Religious minorities, especially Christians, have been repeatedly targeted by terrorists.
Widodo slammed the attacks, telling reporters: "We must unite against terrorism. The state will not tolerate this act of cowardice."