"Ten people died and eight of them have not been identified," spokesman for the East Java Provincial Police Senior Commissioner Frans Barung Mangera told Antara news agency.

Country's President Joko Widodo visited Bhayangkara Hospital to meet victims of the attacks.

"The president made the visit after reviewing two bombing incident locations namely GKI church on Jalan Diponegoro Surabaya and Central Pentecost Church Surabaya on Jalan Arjuna," reported country's Antara news agency.

He has appealed people in the country to remain calm.

"I appeal to all people across the country to remain calm, maintain unity and alertness," he was quoted as saying by the agency.

Indonesia's Foreign Minister Retno Marsudi has condemned the attack.

"Strongly condemn the terrorist attack in Surabaya - Ret We will not back down in the fight against terrorism Let us unite in the fight against terrorism #UniteAgainstTerrorism #WeAreNotAfraid," she tweeted.

The US Embassy in Indonesia also condemned the attacks on the churches.

"The United States strongly condemns this morning’s attacks on three churches in Surabaya. These attacks on peaceful worshipers are an affront to the tolerance and diversity embraced by Indonesians.  The United States stands with the people of Indonesia, and we offer our deepest condolences to the families of the victims," US Embassy said in a statement.

Indonesian investigators have not yet disclosed the names of the suspects behind the attacks. 

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