The United Nations says the death toll from Friday's bombing of the U.N. headquarters in Nigeria has risen to 23 – and another 81 people were wounded in the attack.

U.N. Deputy Secretary-General Asha-Rose Migiro visited some of the wounded Sunday as U.N. and Nigerian officials continue their investigation.

The U.N. security chief said no specific threat had been made against the compound but there had been some general information about an attack.

Witnesses say a suicide bomber forced his car past two security gates to explode inside the sprawling U.N. compound Friday.

A man who identified himself as a spokesman for Boko Haram, a radical Islamic group in Nigeria, told VOA the group is responsible for the bombing.

Nigerian President Goodluck Jonathan has vowed to bring terrorism in his country under control; U.N. Secretary-General Ban Ki-moon has said such acts of terrorism are unacceptable.

Boko Haram has been blamed for many bombings and shootings aimed at authority figures in northeastern Nigeria, mainly in the state of Borno. The group also has claimed responsibility for other bombings, including the June bombing of Nigeria's national police headquarters in Abuja.

The group wants a strict form of Islamic law applied more widely across Africa's most populous nation.