Two people, including a police officer, were killed in a violent incident outside the US Department of Defense headquarters on Tuesday.
According to the head of the Pentagon Police Department, Woodrow Kusse, a member of his unit was attacked in the morning, after which there was an exchange of fire.
The Federal Police FBI have started investigations.
According to later media reports, an attacker killed a police officer with stabs in the neck.
He was then shot dead by other police officers.
The Pentagon is located directly on the Washington city limits in the state of Virginia.
According to official information, the incident took place on the premises of the public transport station at the Pentagon.
There was last a mysterious attack at a checkpoint near a subway entrance in 2010: An armed attacker opened fire at the main entrance to the Ministry of Defense and injured two security guards.
Pentagon cordoned off
The Pentagon was cordoned off for a short time because of the incident on Tuesday morning (local time).
Pentagon spokesman John Kirby said Defense Secretary Lloyd Austin was not in the building at the time of the attack but was kept informed of the situation.
Austin later offered condolences to the relatives of the killed officer and ordered the flags to be raised at half mast over the Pentagon.