WASHINGTON -?US President Barack Obama condemned Monday's shooting at Washington Navy Yard as a "cowardly act" while pledging a thorough investigation into the tragedy believed to have caused multiple deaths and injuries.

"We still don't know all the facts. But we do know that several people have been shot, and some have been killed. So we are confronting yet another mass shooting," said Obama before delivering a speech at the White House marking the 5th anniversary of the financial crisis.

Obama said he has been briefed about the shooting that happened on a military installation in the nation's capital and targeted the military and civilian personnel who would not have expected " the unimaginable violence" here at home.

"We sent thoughts and prayers to all at the Navy Yard that have been touched by the tragedy," the president said, vowing that the federal and local authorities would work closely together to investigate the incident thoroughly and to hold those whoever carried out this "cowardly act" responsible.

The shooting happened at 8:20 a.m. EDT (1320 GMT) when a shooter opened fires inside a building at the Washington Navy Yard that serves as the headquarters of the Naval Sea Systems Command Headquarters, the US Navy said on Twitter.

Obama has been briefed several times on the unfolding situation, said the White House in a statement Monday.

"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 statement.