SAN DIEGO -- The federal courthouse in San Diego will be closed today as workers repair damage caused by a suspected pipe bomb.

The explosion early Sunday damaged the front entrance and lobby area of the Edward J. Schwartz Federal Courthouse, said FBI spokeswoman April Langwell.

No one was hurt by the blast, which happened at 1:40 a.m. and was reported by two guards inside the building.

Debris was found lodged in a window about eight stories up the AT&T building that faces the courthouse. About 40 agents combed the courtyard in front of the courthouse after the area was swept for explosives.

The evidence collected will be sent to an FBI laboratory in Virginia for analysis by bomb experts.

"It's too early to tell if it's terrorism-related," said FBI spokesman Darrell Foxworth. "It does not appear to be right now."

Authorities said surveillance cameras outside the building might provide information, but there are no cameras that directly face the doorway. At the time of the explosion there were not many people around the building, which is a block from nightclubs in the Gaslamp Quarter.

Streets in the area were closed until early Sunday afternoon. The explosion is under investigation and no arrests have been made.

No one has claimed responsibility for the blast, authorities said, and no threats were received before the bomb exploded.