A woman suicide bomber blew up in the midst of a crowded evangelical Christian church service in northeast Nigeria on Sunday and killed at least five people, witnesses said.

It is the latest in a string of bombings and shooting attacks blamed on the Islamic extremist group Boko Haram that has killed some 200 people in the past week.

Nearly 100 men and boys praying in a mosque were gunned down on Wednesday.

Police rushed to the Redeemed Christian Church of God in Potiskum, the largest city in northeastern Yobe state. Wailing women and stunned men wandered aimlessly. One congregant said the blast came from a woman who was in the congregation. She said she was too scared to give her name.

An AP reporter counted five bodies from the blast in the morgue of the local hospital, where a wounded woman was being treated.

Nigeria's President Muhammadu Buhari on Friday condemned the latest attacks as barbaric and said they underline the need for an expanded multinational army to crush the extremists.

Boko Haram took control of a large swath of northeast Nigeria last year and declared an Islamic caliphate. As it stepped up cross-border attacks, Nigeria and its neighbors formed a multinational army that this year drove them out of towns and villages. But bombings and village attacks are increasing as Boko Haram apparently responds to an Islamic State group directive to increase attacks in the Muslim holy month of Ramadan.

At least 13,000 people have died in the 6-year-old Islamic uprising that also has driven 1.5 million people from their homes, some across borders.