BLACKSBURG, Va., April 18 (Reuters) - Police with assault rifles descended on a building at grieving Virginia Tech university on Wednesday, responding to a security alert just two days after a student killed 32 people and then himself.

"We're not going to get into exactly what that is," said Corinne Geller, a state police spokeswoman. "It was not a bomb threat."

Geller said there had been a telephone call reporting suspicious activity at Burruss Hall.

"The suspicious activity was unfounded," she said.

Staff were evacuated from Burruss Hall, next door to Norris Hall where most of the victims died in Monday's shooting rampage, various media outlets reported.

CNN quoted the university's public relations office as saying it was a "suspicious event".

"Everything is okay," a campus police official told reporters.

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