LAGOS, Nigeria - Terrorist attacks across Nigeria by a radical Muslim sect killed at least 39 people, with the majority dying on the steps of a Catholic church after celebrating Christmas Mass as blood pooled in dust from a massive explosion.

Authorities acknowledged Sunday that they could not bring enough emergency medical personnel to care for the wounded outside St. Theresa Catholic Church in Madalla, near Nigeria's capital of Abuja. Elsewhere, a bomb exploded amid gunfire in the central Nigeria city of Jos, and a suicide car bomber attacked the military in the nation's northeast as part of an apparently coordinated assault by the sect known as Boko Haram.

The Christmas violence, denounced by world leaders and the Vatican, shows the threat of the widening insurrection posed by Boko Haram against Nigeria's weak central government. Despite a recent paramilitary crackdown against the sect in the oil-rich nation, Africa's most populous, it appears Nigeria remains unable to stop the threat.

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

The White House condemned what it called a "senseless" attack, offered its condolences to the Nigerian people, and pledged to assist authorities in bringing those responsible to justice.

In a statement, Britain's foreign secretary, William Hague, said: "These are cowardly attacks on families gathered in peace and prayer to celebrate a day which symbolizes harmony and goodwill toward others."

U.N. Secretary-General Ban Ki-moon called in a statement for an end to sectarian violence in the country.

The first explosion struck St. Theresa Catholic Church just after 8 a.m. Sunday, killing 35 people and wounding 52, said Slaku Luguard, a coordinator with Nigeria's National Emergency Management Agency.

Although billions of dollars of oil money flow into Nigeria's budget yearly, Luguard's agency could only send text messages to journalists asking for their help in getting more ambulances.

The wounded filled the concrete of a nearby government hospital, with television images showing them crying in pools of their own blood. The dead lined an open-air morgue.

The bombing and the delayed response drew anger from those gathering around the church after the blast. The crowd initially blocked emergency workers from the blast site, allowing them in only after soldiers arrived.

"We're trying to calm the situation," Luguard said.

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

By noon Sunday, explosions echoed through the streets of Damaturu, the capital of Yobe state, where fighting between security forces and the sect had already killed at least 61 people in recent days. Sunday's most serious attack came when a suicide bomber detonated a car loaded with explosives at the headquarters of Nigeria's secret police, the State Security Service.

The bomber killed three people in the blast, though the senior military commander who was apparently targeted survived the attack, the State Security Service said.

After the bombings, a Boko Haram spokesman using the nom de guerre Abul-Qaqa claimed responsibility for the attacks in an interview with the Daily Trust, the newspaper of record across Nigeria's Muslim north. The sect has used the paper in the past to communicate with the public.

Boko Haram, whose name means "Western education is sacrilege" in the local Hausa language, is responsible for at least 504 killings this year alone, according to an Associated Press count.

Last year, a series of Christmas Eve bombings in Jos claimed by the militants left at least 32 dead and 74 wounded. The sect also claimed responsibility for the Aug. 26 bombing of the U.N. headquarters in Abuja that killed 24 people and wounded 116.