World Council of Churches general secretary Rev. Olav Fykse Tveit has condemned the Sunday suicide bombing attacks at three separate churches during services in Surabaya, East Java, Indonesia.

Pope Francis prayed for the "dear people of Indonesia," and especially Christians in Indonesia's second city of Surabya, saying that he was "particularly close" to them after the deadly attacks.

The East Java police revealed that separate explosions had taken place at Santa Maria Tak Bercela Catholic Church, Diponegoro Indonesian Christian Church and Surabaya Pentecostal Church in and around Surabaya on May 12.

A family of six including two young daughters staged suicide bombings at the three Indonesian churches during Sunday services, killing at least 13 people and at least 40 others in attacks claimed by the Islamic State group, Agence France-Presse reported.

Pope Francis said, "Together let us call upon the God of peace, that He might bring these violent actions to an end; and that in the hearts of all, space might be found for feelings, not of hatred and violence, but of reconciliation and fraternity."

Tveit offered "heartfelt condolences to the people who lost family members and friends."

"It is shocking that this attack was directed against people who were gathered for worship, and that this attack comes on the heels of ongoing violence and persecution," Tveit said.

He said that, "In the face of this brutality, the human family, all people of faith and of good will, must stand together to recommit to respecting and caring for one another, to protecting one another, and to preventing such violence."

The WCC appealed to Joko Widodo, president of Indonesia, to religious leaders and to governments across the region "to act swiftly and boldly to safeguard the fundamental religious rights of worshippers of all faiths/"

It urged them "to ensure security in the face of violence and to guarantee justice for all people. Places of worship representing many different faith traditions have been targets of violence by extremists."

Tveit said, "Government action must be matched by solidarity among Christians, Muslims and people of all faiths as they interact at the local level and together denounce any violent attack."

The WCC head called for prayers, urging the WCC fellowship and others across the world to remain steadfast in their quest for peace and justice for Christians and all who are persecuted.

"Through prayer, action and unity, we can bring a powerful force of love in the wake of terror and violence," he said.

One of the attacked churches is a parish church of a WCC member church, Diponegoro Indonesian Christian Church.

More than 87 percent of people in Indonesia are Muslims, while Christians are beleived to account for about 10 percent of the 260 million people there.