An explosion ripped through a Catholic church during Christmas Mass near Nigeria’s capital on Sunday, killing at least 25 people, officials said. A second explosion later went off near another church in the restive city of Jos, raising fears that a radical Muslim sect was to blame.

There was no immediate claim of responsibility for the blasts, but the explosions come amid a wave of attacks in Nigeria by Boko Haram, which has been blamed for at least 465 killings this year alone. Last year a series of Christmas Eve bombings in Jos that were claimed by the militants left at least 32 dead and 74 wounded.

The first explosion on Sunday struck St. Theresa Catholic Church in Madalla, a town in Niger state close to the capital, Abuja, authorities said. Rescue workers recovered at least 25 bodies from the church and officials continued to tally those wounded in various hospitals, said Slaku Luguard, a coordinator with Nigeria’s National Emergency Management Agency.

His agency already has acknowledged it didn’t have enough ambulances immediately on hand to help the wounded. Mr. Luguard also said an angry crowd gathered at the blast site hampered rescue efforts as they refused to allow workers inside.

“We’re trying to calm the situation,” Mr. Luguard said. “There are some angry people around trying to cause problems.”

In Jos, a second explosion struck near a Mountain of Fire and Miracles Church, government spokesman Pam Ayuba said. Mr. Ayuba said gunmen later opened fire on police guarding the area, wounding one police officer. Two other locally made explosives were found in a nearby building and disarmed, he said.

“The military are here on ground and have taken control over the entire place,” Mr.Ayuba said.

The city of Jos is located on the dividing line between Nigeria’s predominantly Christian south and Muslim north. Thousands have died in communal clashes there over the last decade.

The U.S. Embassy in Nigeria’s capital of Abuja had issued a warning on Friday to citizens to be “particularly vigilant” around churches, large crowds and areas where foreigners congregate.

Several days of fighting in the northeast between the sect and security forces already had killed at least 61 people, authorities said.

In the last year, Boko Haram has carried out increasingly bloody attacks in its campaign to implement strict Shariah law across Nigeria, a nation of more than 160 million people.

Boko Haram claimed responsibility for a November 4, 2011 attack on Damaturu, Yobe state’s capital, that killed more than 100 people. The group also claimed the Aug. 24 suicide car bombing of the U.N. headquarters in Nigeria’s capital that killed 24 people and wounded 116 others.

While initially targeting enemies via hit-and-run assassinations from the back of motorbikes, violence by Boko Haram now has a new sophistication and apparent planning that includes high-profile attacks with greater casualties. Boko Haram has splintered into three factions, with one wing increasingly willing to kill as it maintains contact with terror groups in North Africa and Somalia, diplomats and security sources say.

More In: International | News