Churches in Nigeria are regular targets for Muslim militants. (Reuters)

Twin suicide car bombs exploded Sunday at a church inside one of Nigeria's top military bases, killing at least 11 people and wounding another 30 in an embarrassing attack showing the continued insecurity that haunts Africa's most populous nation.

No one immediately claimed responsibility for the attacks, but suspicion immediately fell on the radical Islamist sect known as Boko Haram, whose suicide bombers target Sunday worship services in what has become a weekly macabre routine in Nigeria.

This attack in Jaji on Sunday, however, happened inside a barracks home to the Armed Forces Command and Staff College, one of the country's most important military colleges. It also showed a new dangerous sophistication as the second explosion appeared timed to target responders rushing to aid the wounded 10 minutes after the first blast, officials said.

Bus rammed church walls before exploding

The attack began just after noon and targeted the St. Andrew Military Protestant Church, Brig. Gen. Bola Koleoso said. A bus loaded with explosives somehow made it inside the barracks' perimeter and rammed into the church's walls before exploding, Koleoso said.

The second blast came from a sedan parked nearby and struck in the chaos afterward as emergency workers, soldiers and survivors of the first blast milled around the church, he said.

"Investigation into the bombings have commenced and the area already (has been) cordoned off," Koleoso said in a text message sent to journalists after the attack.

The military kept journalists away from the scene of the blast and took the wounded to military clinics, limiting independent verification of what happened in the attack. Yushau Shuaib, a spokesman for Nigeria's National Emergency Management Agency, would only say an explosion happened at the base and referred all questions to the military.

Nigerian military downplays casualty figures

Nigerian security forces, particularly the military, routinely downplay casualty figures in attacks, so the true scope of the attack may never be known. However, this isn't the first time that a major military base has been struck during the increasingly bloody guerrilla fighting waged by Boko Haram.

On New Year's Eve in 2010, a bomb allegedly planted by the sect exploded at a crowded and popular outdoor beer garden at a military barracks in Nigeria's capital, Abuja, and killed at least four people.

Sunday's attack targeted Jaji, which teaches the top military minds in Nigeria. The area sits just north of the city of Kaduna, a major city in Nigeria's north that sits on the uneasy dividing line between the country's predominantly Christian south and Muslim north.

Religious violence and rioting in the city has killed thousands since Nigeria became a democracy in 1999. Most recently, a suicide car bombing in October at a Catholic church in the city killed at least seven people and wounded more than 100 others.

While several suicide car bombings in Kaduna this year have gone unclaimed, many believe them to be the work of Boko Haram, whose name means "Western education is sacrilege" in the Hausa language of Nigeria's north.

Boko Haram is blamed for more than 760 killings this year alone, according to an Associated Press count. The group has said Nigeria must implement strict Shariah law and free its imprisoned members before it will stop its attacks.

Western diplomats and military officials say the sect has loose ties to both al Qaeda in the Islamic Maghreb and Somalia's al-Shabab, while also offering fighters to join Islamists now controlling northern Mali. That has led to worries the group will grow only more violent as time goes on.

Despite sending soldiers into troubled northern cities, Nigeria's military has been unable to stop the attacks and has alienated locals with heavy-handed tactics and retaliatory attacks that have seen dozens of civilians killed at a time.

Sunday's attack in Jaji came only two days after a special military taskforce announced that it would offer $1.8 million in rewards for information that could lead to the arrest of top Boko Haram members.