Police closed a highway near the Pentagon as the investigation into the shots continued Shots were fired at the Pentagon, hitting the building and causing minor damage, US officials have said.
Police temporarily closed some roads and pedestrian entrances after a civilian reported he might have heard shots before dawn near the south entrance of the building.
A sweep of the defence department headquarters found some shots had hit the building.
There were no injuries, Pentagon spokesman Marine Col Dave Lapan said.
Mr Lapan said he did not know how many shots had been fired or what kind of weapon had been used.
Roads and pedestrian entrances to the Pentagon were re-opened soon after the incident. Part of a highway near the Pentagon was later closed as the investigation continued.
Police were spotted searching a grassy area on the south side of the building, the Associated Press news agency said.
Bullet holes were also discovered on Monday in the windows of the National Museum of the Marine Corps, about 30 miles (50km) south of the Pentagon.
Mr Lapan said he did not know if there was any connection between the two incidents.
Tuesday’s investigation at the Pentagon comes about seven months after a gunman shot and wounded two security officers at a security checkpoint into the building.
The 36-year-old shooter, John Patrick Bedell, was shot by police and died hours after being admitted to a hospital in critical condition.
Security measures at the Pentagon were tightened following the March shoot-out.
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