ZURICH (REUTERS) - Swiss police said on Friday they were investigating an anonymous bomb threat at the Fifa congress in Zurich that led authorities to search the premises.

The threat was made by telephone to a Zurich-based newsroom on Friday morning, Zurich city police said, adding that no one had been evacuated from the congress.

However, participants in the world football congress, which paused for lunch 45 minutes earlier than expected, were initially denied re-entry into the auditorium while officers conducted a search, a witness said.

"A search was carried out. The premises have been cleared by the authorities," Fifa secretary-general Jerome Valcke told the congress after it resumed.

Congress participants and media representatives were let back into the auditorium following the search, with no additional security precautions.