At least 11 people, including a suicide bomber, were killed and 41 injured on Sunday in bomb attacks on three churches in the Indonesian city of Surabaya, police said.
The first explosion took place in Surabaya's Santa Maria church, killing four people, including the suicide bomber.
Almost immediately afterwards, there were explosions in a protestant church on the Diponegoro street, where two people were killed, and another one at a pentecostal church on Arjuno street, where another two people died.
Another person died later in a hospital in Surabaya. The police are yet to release details of the other two victims.
The bomb disposal squad diffused another bomb outside the Diponegoro church.
Hundreds of police and anti-terrorism squad personnel have been deployed to the attack sites, while broken glass and burned vehicles paved the road outside the churches.
Wawan Hadi Purwanto, the Communication Director at the State Intelligence Agency said that one of the attackers could have been a women and they suspected that the Islamist rebel group Jemaah Ansharut Daulah -- inspired by the Islamic State -- was behind the attack.
Indonesia, where Muslims constitute 88 per cent of the population of 260 million, is on high alert in the weeks leading up to the holy month of Ramadan, which begins in two days. Islamist terrorists have in the past carried out attacks during this period.
The country has witnessed a number of terrorist attacks, including one on the island of Bali, a major tourist hotspot, where 202 people were killed in an attack in 2002.