Washington, Oct 20: Someone fired shots at the Pentagon on early Tuesday in what U.S. security officials described as “a random event.”

No one was injured in the pre-dawn incident in which shots were fired into two windows at the sprawling Defense Department just across the Potomac River from Washington.

Steven Calvery, director of the civilian Pentagon Force Protection Agency, told reporters that authorities would have to re-evaluate their assessment if they find the incident was part of a larger plot. He said authorities did not yet have any suspects.

Mr. Calvery said a number of his officers reported hearing five to seven shots fired at about 4:55 a.m. EDT near the south parking lot of the Pentagon. The building, and roads leading to the property, was shut down as officers did an initial sweep of the area. They were reopened 45 minutes later.

An internal search of the building found fragments of two bullets still embedded in two windows — one on the third floor and one on the fourth. The bullets had shattered, but did not penetrate, the windows, Mr. Calvery said. The windows were part of offices that are being renovated and they were unoccupied at the time.

He said he did not know what kind of weapon was used but that it was probably a high-velocity rifle.

Officials said it was the first incident of its kind since early March, when a gunman opened fire at a security checkpoint into the Pentagon in a point-blank attack that wounded two police officers.

State, federal and local agencies were cooperating in Tuesday’s investigation in which authorities were studying surveillance video and questioning witnesses. Mr. Calvery said they were looking at whether the shooting might be related to Sunday’s discovery of bullet holes in windows at the National Museum of the Marine Corps some 50 kilometres south of the Pentagon. That shooting also is believed to have been with a rifle and possibly during early morning hours.

The Pentagon agency was working with the FBI and local police who helped conduct the sweep of the area and Virginia State Police who closed part of a nearby major highway in the search of evidence. A dozen officers walked side-by-side in a line as they combed through a grassy area on the south side of the building at midmorning.

Mr. Calvery said that in addition to his officers, investigators also were talking to some construction workers who also heard the shots.