The FBI is helping authorities in the Cincinnati area investigate recent bomb threats at high-profile local venues.

FBI spokesman Todd Lindgren told The Associated Press on Sunday that agents are working with other law enforcement on the threat probe.

City spokesman Rocky Merz says an anonymous caller Saturday claimed an explosive device had been planted on one of Cincinnati’s streetcars, which officially began operation Friday. Service was halted temporarily while a bomb-sniffing dog was used.

No explosives have been found.

Merz urges public help for identifying those behind the hoaxes.

Police evacuated some 10,000 fans at the end of a prep football game in the northwest Cincinnati suburb of Colerain Township and a game was postponed Friday night in the northeast suburb of Mason. The Cincinnati Zoo was evacuated Thursday.

(AP)