LAGOS, Nigeria (AP) _ Terror 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 on Sunday acknowledged they could not bring enough emergency medical personnel to care for the wounded outside St. Theresa Catholic Church in Madalla near Nigeria's capital. 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 Day 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, it appears that Africa's most populous nation remains unable to stop the threat.

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 symbolises harmony and goodwill towards others.''

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

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

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

Those wounded filled the cement floors of a nearby government hospital, with television images showing them crying in pools of their own blood. Corpses 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, only allowing them in after soldiers arrived.

``We're trying to calm the situation,'' Luguard said. ``There are some angry people around trying to cause problems.''

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 already had killed at least 61 people in recent days. The most serious attack on Sunday came when a suicide bomber detonated a car loaded with explosives at the state headquarters of Nigeria's secret police, the State Security Service.

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

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 newspaper in the past to communicate with public.

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 group, 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.

This Christmas attack comes a year after a series of Christmas Eve bombings in Jos claimed by the militants left at least 32 dead and 74 wounded. The group also claimed responsibility for the Aug. 26 bombing of the United Nations headquarters in Nigeria's capital Abuja that killed 24 people and wounded 116 others.

The sect came to national prominence in 2009, when its members rioted and burned police stations near its base of Maiduguri, a dusty northeastern city on the cusp of the Sahara Desert. Nigeria's military violently put down the attack, crushing the sect's mosque into shards as its leader was arrested and died in police custody. About 700 people died during the violence.

While initially targeting enemies via hit-and-run assassinations from the back of motorbikes after the 2009 riot, violence by Boko Haram now has a new sophistication and apparent planning that includes high-profile attacks with greater casualties. That has fueled speculation about the group's ties as it has splintered into at least three different factions, diplomats and security sources say. They say the more extreme wing of the sect maintains contact with terror groups in North Africa and Somalia.

Targeting the group has remained difficult, as sect members are scattered throughout northern Nigeria and nearby Cameroon, Chad and Niger. Analysts say political considerations also likely play a part in the country's thus-far muted response: President Goodluck Jonathan, a Christian from the south, may be hesitant to use force in the nation's predominantly Muslim north.

In a statement, Jonathan condemned the blasts as a ``unwarranted affront on our collective safety and freedom.''

``I want to reassure all Nigerians that government will not relent in its determination to bring to justice all the perpetrators of today's acts of violence and all others before now,'' Jonathan said.

However, Jonathan has made the same promises after a series of spiraling attacks by the group. His spokesman, Reuben Abati, defended the president by saying the country planned to spend more on security and had made arrests targeting the group.

``The administration is very determined to address this new threat of terrorism that seems to have slipped into our environment,'' Abati told the AP.

But anger continues to grow over the sect's apparent ability to strike at will _ anger that could be seen at St. Theresa Catholic Church. After the blast, someone picked up a burnt piece of wood to scrawl: ``Revolution now in the country'' on its cement walls.