Nigerian authorities say a man with links to al-Qaida helped orchestrate last week's bombing of the U.N. headquarters in Abuja that killed 23 people.

The Nigerian State Security Service said Wednesday that Mamman Nur, a member of the radical Islamist sect Boko Haram, masterminded the attack while working “in concert” with two other suspects who have been arrested.

The statement says Nur had recently returned from Somalia, where al-Qaida agents have helped insurgent group al-Shabab fight the Somali government.

Nur remains at large. Nigerian authorities did not identify the two suspects in custody but said they are members of Boko Haram and have made “valuable statements.”

Last Friday, a suicide bomber detonated a car bomb inside the U.N. Abuja compound, wounding more than 80 people in addition to the 23 deaths.

A man who identified himself as a Boko Haram spokesman told VOA that the group was responsible for the attack.

Boko Haram, whose name means “Western education is sinful,” has been blamed for many bombings and shootings of authority figures in northeastern Nigeria, mainly in the state of Borno. The group has also claimed responsibility for attacks in Abuja, including a June bombing outside Nigeria's national police headquarters.

The group wants a strict form of Islamic law applied more widely across Nigeria.

Nigerian President Goodluck Jonathan has vowed to increase security and bring terrorism in the country under control.