NEW HAVEN, Connecticut -- Authorities investigating an explosion in a Yale University law school classroom said it was generated by a pipe bomb.
The bomb, which shook the building about 4:40 p.m. EDT, did not cause any injuries. It damaged the empty classroom where it exploded, blowing out a wall while leaving the windows intact, authorities said.
The blast came a day after the national terror threat level was raised to high.
The FBI has dispatched its joint terrorism task force to the scene, but law enforcement officials said there is no indication the explosion was terror-related.
New Haven Mayor John DeStefano said nothing indicates that the bombing was anything other than "a limited event." No controversial speakers were on campus around the time of the explosion, he said.
"The suggestion is that something was placed in a vacant classroom," DeStefano said, adding that investigators would not comment on whether a timing device was used.
FBI Special Agent Mike Wolf said no one has claimed responsibility for the bombing and there were no threats before the blast. Wolf said investigators will examine forensic evidence and try to interview anyone who was in the building near classroom 120 around the time of the blast.
Law student Tali Farhadian said she was studying for an exam in a classroom when the blast went off.
"We just heard an extremely loud sound. It sounded like walls really were just coming down or like a ceiling was falling or something," she said. "I had never heard anything like this before."
Yale University vice president Linda Lorimar said during her 25 years at Yale, she was not aware of any threats against the school.
"The main entrance [to the building] has a person who stands at a sort of an information desk, but it's pretty much open to anybody," said law student Sari Bashi. "There are often lectures and public events there, so anybody can walk in, more or less."
Much of the campus was empty, with undergraduate classes already done for the year. Some graduate students are still on campus, taking exams. Commencement is scheduled for Monday.
"It's exam period and most exams take place in the morning, so if you were going to try to hurt somebody, you wouldn't pick this particular room at 4:45 [p.m. EDT] on this day," Bashi said.
The law school will be closed Thursday and Friday with scheduled exams occurring in another building and the rest of the university will operate normally, a university statement said.