WASHINGTON (AP) — A lockdown was underway Thursday morning across the Washington Navy Yard campus after reports of shots fired, but a senior law enforcement official said those reports had not been confirmed.

The building where the shots were reported was already largely emptied Thursday as civilian and military law enforcement officers swept it, said the official, who was receiving detailed briefings on the situation but spoke on condition of anonymity because the person was not authorized to discuss developments with reporters.

The official also says there have been no reports of injuries.

The building is the same one where a gunman killed a dozen workers in a rampage two years ago, according to a second official — a federal one who spoke on condition of anonymity for lack of authorization to discuss details publicly.

A heavy police and fire department presence began blocks away from the Navy Yard, with roads blocked and a helicopter hovering overhead.

In September 2013, military contractor Aaron Alexis killed 12 civilian workers at the Navy Yard's Building 197 before he was fatally shot by police. The building has since been renamed the Humphreys Building. It reopened this year.

The Navy Yard, in southeast Washington, is the country's oldest naval installation.