A late-morning bomb threat called in to the Vicksburg Warren County E911 Communications Center forced Vicksburg police to close and evacuate the U.S. Post Office on Pemberton Square Boulevard and Vicksburg High School Wednesday, authorities said.

Deputy Vicksburg police chief Bobby Stewart said the call came into the dispatch center about 11:58 a.m.

“All the caller said was they had dropped a bomb at the post office and Vicksburg High School and hung up,” he said. “We had no other information. We are trying to determine who made the call.”

Stewart would not say if a man or woman made the call.

Students at Vicksburg High School were evacuated from the school and remained outside for more than an hour before police officers and X-on, the police department’s explosive detection dog, were able to search the buildings and clear the school.

The post office was closed for more than two hours before a search cleared the building. Stewart said the delay was longer than the school because post office officials had to wait for the postal inspector to arrive from Jackson and approve the reopening.