ISLAMABAD, Pakistan - A suicide bomber was responsible for the Monday blast at a United Nations office in Islamabad which left three people including a foreign national dead, a senior police official said.

"It was a suicide blast," Bani Amin, deputy inspector general of police operations, said at the scene.

"We have recovered legs and the skull of the suicide bomber. We are investigating how he managed to enter inside the building. There are scanners, there are cameras and strict security arrangements."