(CNN) -- Nigerian authorities said Wednesday that a man with ties to al Qaeda plotted last week's car bombing at the United Nations' headquarters in the Nigerian capital that killed 23 people.
The Nigerian State Security Service said Mamman Nur recently returned from Somalia and was "working in concert" with two other suspects who have been arrested. The militant Somali group Al-Shabaab has been linked to al Qaeda.
The secret service described Nur as a "notorious Boko Haram element." Boko Haram, a militant Islamic group, aims to enforce a strict version of Islamic law in Nigeria.
The militant group had claimed responsibility for the attack in which a Honda packed with explosives rammed into the U.N. building, shattering windows and setting the place afire.
Abuja has suffered a spate of deadly 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 attacks on the church and police station may have been the work of Boko Haram, officials said.
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.