An explosion apparently caused by a suicide bomber in the lobby of the World Food Program office in Islamabad killed at least three people — one foreigner and two Pakistani women — and wounded eight others on Monday, according to police and United Nations officials.

Ishrat Rizvi, the spokesperson for United Nations operations in Islamabad, said that all U.N. offices in Pakistan were closed immediately as a precaution.

“This is a temporary arrangement to ensure the safety and security of our staff,” she said by telephone.

There was no immediate claim of responsibility.

Police officials said the explosion was apparently triggered by a suicide bomber, suggesting a serious security breach in a building tightly guarded by private security officers.