WASHINGTON – Up to three gunmen, at least two dressed in military-style clothing, killed several people and wounded many others in a shooting spree at the US Navy Yard on Monday, officials said. A suspected gunman was among the dead and Washington D.C. police said they were searching for two other possible shooters they described as one white man and one black man. Officials said not all the facts were immediately known about the shooting that began at about 8:36 a.m. EDT (1236 GMT). President Barack Obama said he is mourning “yet another mass shooting” and called it a “cowardly act.” The shooting led to tightened security at the Capitol nearby. Authorities identified the dead shooter as a Navy employee whose work status had been changed earlier this year, said a federal government official who spoke only on condition of anonymity because he wasn't authorized to speak on the record. While that may suggest the motive was job related, authorities haven't ruled out anything including terrorism, the official said. Washington Police Chief Cathy Lanier said she didn't think the other gunmen were part of the military. Washington police declined to give a number of fatalities, saying there were “multiple victims deceased inside” the Naval Sea Systems Command headquarters, just 2.6 miles (4 km) from the White House. Among the injured were a District of Columbia police officer, who was in stable condition in surgery, and one other law enforcement officer, officials said. “There was three gunshots straight in a row,” said Patricia Ward, who works at the Navy Yard, describing how she first heard the gunfire while having breakfast at the headquarters building. A few seconds later, Ward said she heard four more gunshots. Security guards rushed in and got people out as fast as they could – “‘Run, run, run,' they told people,” Ward told reporters. Helicopters circled the headquarters with some touching down on the building's roof, according to a live feed by Washington's WJLA TV. The Federal Aviation Administration said it briefly suspended departures at Reagan National Airport. The District of Columbia Public Schools have put six schools and an administration building on lockdown as a precaution. The White House urged citizens to follow instructions from authorities and first responders. The Washington Navy Yard is the oldest shore facility of the US Navy. A former shipyard and ordinance plant, the facility in southeast Washington is currently home to the Naval Sea Systems Command, Navy museum and other facilities. – Agencies