At least 13 people are dead after a shooting at a Navy shipyard in the US capital Washington DC today.
The first shots were fired just before 8:20 am (1:20pm UK time) in a building at the Navy complex, around a mile from the seat of US government.
The suspected gunman, identified by the FBI as 34-year-old Aaron Alexis, was among the dead at the scene. The FBI would also like to question one further suspect.
A dozen or more people, including a police officer and at least two Navy employees, are recovering from their injuries in hospital.
ITV News' Washington Correspondent Robert Moore reports:
The background and motive of the shooting suspect Aaron Alexis remain cloudy.
Media reports suggest he worked for the Navy Reserve in Fort Worth, Texas for almost four years, before being discharged in January 2011 for unknown reasons.
It is not known how he entered the Navy base in Washington, or whether he was working there as a civilian contractor or otherwise.
As the FBI scours the scene of the shooting for clues, another potential suspect remains at large.
Police want to question an unnamed black male, described as being 40-50 years old and wearing a military-style uniform, about his possible involvement.
A second man was originally wanted for questioning, but is no longer a suspect.
SWAT teams and dozens of armed police officers descended on the Navy base within minutes of the shooting being reported.
Armed security personnel were seen on a roof at the complex, and a police helicopter was used to carry at least one of the wounded people from the scene.
At least 10 schools in the surrounding areas were put "on lockdown" and local residents were asked to remain indoors.
Enhanced security measures were also put in place at the Capitol building and Senate, although there was no known threat.
There has been widespread condemnation of whoever carried out the shooting, with the Navy Secretary calling it a "stunning and horrific blow" to the Navy family.
President Barack Obama regretted that America was "confronting yet another mass shooting".
His attempt to toughen gun control regulations in light of the Sandy Hook school shooting in Connecticut last December met with strong opposition in Congress.
Today's incident follows another shooting at Fort Hood military base in 2009 in which 13 people were killed and more than 30 injured by a lone gunman.