(CNN) -- A Nigerian militant group has claimed responsibility after a car loaded with explosives rammed into the United Nations' building in the capital, killing 23, a government spokesman said Monday.
The suicide attack Friday shattered windows, set the building ablaze and left gaping holes on the walls.
Radical Muslim sect Boko Haram, which aims to enforce a strict version of Sharia law, has claimed responsibility, said Reuben Abati, the government spokesman.
Eighty-one people were injured, he said.
The attack targeted a building that housed 26 U.N. humanitarian and development agencies, U.N. Secretary-General Ban Ki-moon said last week. The Liberian and U.S. embassies are also nearby.
"This was an assault on those who devote their lives to helping others," Ban said.
Nigerian President Goodluck Jonathan described the suicide bombing as "barbaric, senseless and cowardly" and intensified security around the capital.
The capital of Abuja has experienced a series of bombings in recent months.
In June, a car blast killed at least five people at the police headquarters in the city.
A month later, at least three people died in an explosion near a church outside the capital. The number of casualties could have been higher if services had still been going on, according to a police spokesman.
The attacks on the church and police station may have been the work of Boko Haram, the nation's officials said this year.
Africa's most populous nation is divided between a largely Christian south and a Muslim north.
"Boko Haram" translates loosely as "Western education is forbidden/sinful."
The group holds all government authority in contempt and wants to establish a Sharia state in northern Nigeria.
Boko Haram has been running religious schools for years, but did not rise to national prominence until it attacked police stations and prisons two years ago.
In retaliation, security forces launched a fierce crackdown that destroyed the group's camp and led to the arrest of its leader, Mohammed Yusuf.
He died in police custody.