Pentagon File photo:VCG

The Federal Bureau of Investigation (FBI) identified Wednesday the attacker who killed a police officer on a bus platform at the Pentagon and forced the US Defense Department into lockdown, but gave no motive for the attack.

The FBI said that 27-year-old Georgia native Austin William Lanz got off a bus on Tuesday morning and "immediately, without provocation" stabbed Pentagon Force Protection Agency officer George Gonzalez with a knife, just yards (meters) from the entrance of the highly secure military headquarters.

"A struggle ensued, in which the subject mortally wounded Officer Gonzalez and then shot himself with the officer's service weapon," the FBI said in a statement.

Other officers then got involved, and Lanz died at the scene, the FBI said. It did not say if the officers also shot Lanz, but witnesses said there was a volley of gunfire in the incident.

Gonzalez was rushed to the hospital but did not survive.

A bystander was also injured but taken to hospital with minor injuries and later released, the FBI said.

No motive was suggested for the attack. Lanz, of Acworth, Georgia, had a long list of arrests according to local Georgia news reports citing court records.

He had been charged with attacking a police officer, making terroristic threats and burglary, among other offenses.

According to the Atlanta Journal-Constitution, he was out on bail and had been ordered by a judge to be evaluated for mental health and substance abuse.

AFP