One suspect was taken into custody after a shooting incident at Pentagon Thursday night, and police suspected there is a second person involved in the case.

The suspect's nationality is American, Pentagon Police Chief Richard Keevill told reporters at a news briefing near the crime scene outside the sprawling Pentagon building, without giving other details of the person's identity.

Two police officers sustained non-life-threatening injuries in the incident.

The police chief said the suspect showed neither emotion nor distress as he approached the police officers at around 6:40 p.m. local time (2340 GMT) in the Metro station outside the Pentagon building.

The person "looked very cool" and didn't speak a word, said Keevill.

When police asked for ID, he reached for his pocket, but pulled out a gun before shooting the officers.

Keevill refused to talk about the specifics of the weapon, nor did he say how many shots were fired.

The suspect's motives are unknown and police are chasing multiple leads, he said.

The wounded officers are with the Pentagon Force Protection Agency, according to Chris Layman, spokesman for the agency.

The two officers who wore protective vests at the time sustained non-life-threatening injuries. They fired back, critically wounding the suspect.

The shooting scene was cordoned off and surrounded by a large number of police officers and patrol vehicles, according to Xinhua reporters at the scene.

After the shooting, the Pentagon was locked down with all entrances closed.

CNN said FBI agents were seen on the scene. TV footages showed heavily armed security personnel were sweeping the scene with M4A1 rifles.

Most entrances to the Pentagon reopened later that night, but the Pentagon Metro entrance and the Pentagon Metro rail and bus facility remained closed, according to a Pentagon statement.

Law enforcement officers say there's no immediate sign of terrorism, and they are investigating a second man who may have accompanied the suspect.

Pentagon is a huge, five-sided office complex in Arlington County, Virginia, just outside Washington, DC. The building houses U.S. Defense Department.

The Pentagon is the world's largest office building by floor area. On Sept. 11, 2001, hijacked American Airlines Flight 77 crashed into the western side of the Pentagon building, killing 189 people, including 64 people aboard the plane and another 125 in the building.

The subway station, where the shooting occurred, is immediately adjacent to the Pentagon.

After a redesign following the 9/11 attack, subway passengers can no longer enter the building directly.

An escalator will send them from the underground Metro station to the ground, where a security check outside the building awaits them.