New York: A bomb exploded in the law school building at the prestigious Yale University campus in Connecticut state, sending security agencies into a tizzy, hours after the US went on a heightened alert against terrorist attacks.

Federal Bureau of Investigation (FBI) is investigating the blast, which occurred at 2.10 am (IST), damaging the classroom and adjacent lounge, with no injuries being reported. However, no immediate link with international terrorism has been established.

But officials said they were not yet sure how sophisticated was the device, who planted it or what was the motive.

No one has claimed responsibility for the blast.

NBC television network quoted investigators as saying that preliminary analysis indicated that it could be a pipe bomb. The FBI said the explosion was caused by an "explosive device".

The explosion triggered concern as it came hours after the nation went on high alert against possible terrorist attacks. But officials moved quickly to allay the fears.

Police cordoned off the area keeping reporters three blocks away, as dogs searched the campus for any more explosive devices.

The bomb exploded in the classroom where law students had taken final examination earlier. The building was almost empty when the blast occurred.

Reports said two classrooms were heavily damaged and one wall collapsed as a result of the blast, which sent glass and debris flying.

PTI