ABUJA, Nigeria (AP) — A large explosion struck a United Nations building in Nigeria’s capital of Abuja on Friday, with one complete wing of the building leveled by the blast, witnesses said. A U.N. official in Geneva called it a bomb attack.

Witnesses told The Associated Press on Friday that the blast happened just before 11 a.m. in the same neighborhood as the U.S. Embassy and other diplomatic posts in Nigeria’s capital. They say many are feared dead.

Police and the wounded thronged the three-story building as people began to search for victims.

Local police spokesman Jimoh Moshood confirmed the blast, but said police were still investigating the cause.

Alessandra Vellucci, a spokeswoman for the U.N. office in Geneva, said the global body’s offices in Abuja had been bombed.

She told The Associated Press that there was no word yet on casualties.