Dozens die in Nigeria church bombs

• The first two bombings happened in the town of Zaria
• A third occurred later in the city of Kaduna
• Christian youths react violently after the blasts

Abuja, Nigeria (CNN) -- At least 15 people were killed and 32 others injured Sunday in three church bombings in northern Nigeria, the country's top emergency official said.

The first two bombings occurred within minutes of each other in the town of Zaria in Kaduna state, said Mohammed Sani Sidi, director-general of the National Emergency Management Agency.

Lucy Bello, a member of the EWCA Goodnews Wusasa Zaria church, said the explosion occurred about 9 a.m., as she was walking into the building. A suicide bomber drove at high speed through a barricade at the church, she said.

Bello, who had bruises from the blast, said she saw a number of people on the ground, some dead and others seriously wounded.

Within minutes, another explosion occurred at the CKC Catholic Church in Zaria, according to the National Emergency Management Agency.

And an hour and a half later, the Sharon Church in the city of Kaduna, about an hour away, was bombed, agency officials said.

Christian youths in Zaria and Kaduna reacted violently, burning tires and blocking major roads. The Kaduna state government imposed a 24-hour curfew.

The bombings are the latest in a string of violence directed at churches. A week ago, a car bomb killed five people during services at a church in Jos, also in northern Nigeria. Angry crowds wielding makeshift clubs fought with police after chasing security forces away from the destroyed church. Three more people died in the clashes.

And two weeks ago, two church bombings in the region killed at least 15 people.

No one immediately took responsibility for Sunday's attacks.

The militant Islamist group Boko Haram has previously carried out attacks, including at churches.

The group also refers to itself as the "Nigerian Taliban" and seeks to overthrow the government and replace it with a regime based on Islamic law.

"Boko Haram" means "Western education is forbidden."

CNN's Nana Karikari-apau and journalist Safiya Akau contributed to this report.