Police discovered a bomb Monday just outside the City Library, thanks to a tip from a city employee.

The employee reported a "suspicious item" on the ground below a library window around 2 p.m., police spokesman Gerald Nielsen said.The suspicious item turned out to be a bomb that apparently had been attached to a library window but fell to the ground. The bomb, in a small black box about the size of a 3-by-5-inch file-card holder, apparently ignited but did not explode, Nielsen said.

It did not cause any damage or injuries. No one has claimed responsibility.

"It had been there for several days," Nielsen said. "It had been observed by someone else prior (to Monday) who didn't know what it was."

Nielsen would not disclose what kind of bomb it was or the amount of explosives it contained. Orem Police are the investigating the incident. The department has asked the federal Bureau of Alcohol, Tobacco and Firearms to analyze the bomb.

Also, Orem police have identified two boys responsible for making four bomb threats over several days to two Orem schools, Nielsen said. There is no association between the calls and the bomb found Monday at the Orem Library.

The boys called a high school and an elementary school, claiming there was a bomb at each school. The students have been disciplined.