Thirteen people have been killed and several others wounded after shots were fired at the Washington Navy Yard, one of the biggest naval command buildings in the United States Monday morning.

The shootings started at around 8:20 a.m. (Eastern Time) when shots were fired at the Naval Sea Systems Command headquarters building where nearly 3,000 people work.

The suspected shooter, identified by the FBI as Aaron Alexis, was killed in a gun battle with the police.

Initially, authorities thought there were two other gunmen at large and were searching for suspected shooters wearing military style clothing.

However, D.C. Metropolitan Police chief, Cathy Lanier, later announced that investigators were confident Alexis was the only one involved in the incident.

The Sea Systems Command is the biggest of the US Navy’s five such facilities and is responsible for building, buying, and maintaining ships and submarines.

Police officers closed streets near the Navy Yard and a “shelter in place” order was issued for the personnel.

US Capitol Police, responsible for protecting the US Congress, confirmed enhanced security at Capitol Hill.

An unnamed White House official has told The Washington Post that President Barack Obama has been briefed on the situation.

“The President directed his team to stay in touch with our federal partners, including the Navy and FBI, as well as the local officials. We urge citizens to listen to the authorities and follow directions from the first responders on site,” said the administration official.