WASHINGTON, Sept 16: Gunmen dressed in military-style uniform shot dead at least 11 people and wounded 14 at the Washington Navy Yard on Monday while the chief of US Naval Operations was inside the complex.

One gunman was also killed as police returned fire, while two others escaped.

Those wounded in the attack were moved to nearby hospitals where officials said most of them were “out of danger”.

The attack spread the fear of another terrorist attacks on the US capital as neighbourhood schools closed and flights taking off at a nearby airport were suspended.

Terrorists had targeted the headquarters of the US defence forces, the Pentagon, in the Sept 11, 2011 terrorist attacks. Monday’s was the first major attack on a US military installation in Washington since 9/11.

In a statement issued by his office, President Barack Obama pledged to punish those responsible. “We will do everything in our power to make sure whoever carried out this cowardly act is held responsible,” he said.

Washington DC Police Chief Cathy Lanier told a mid-day news conference that one suspect was killed in the firing but two others escaped.

She described one suspect as a white male wearing a khaki tan military uniform and a beret, and carrying a handgun. The other is a black man, about 50, wearing an olive military-style uniform, and possessing a “long gun”.

A US Navy spokesman, Commander Ryan Perry, told an afternoon briefing in Washington that Admiral Jonathan W. Greenert, the chief of Naval Operations, was inside the complex when the shooting started. He and his wife, Darleen Greenert, were evacuated safely to the Pentagon.

Mr Greenert is a four-star admiral and member of the US Joint Chiefs of Staff.

While confirming that one of the gunmen was among the 12 dead, police said the dead shooter had an assault rifle, and possibly a shotgun.

Police also said witness accounts and surveillance video indicate that there were more than three shooters and warned that all the weapons used in the shooting were not accounted for.

Two police officers were also wounded in the firing.

The firing started at around 8: 20 am when people were coming to work and the area’s schools had just opened. Ten public and charter schools were placed on lockdown as a precaution, and flights out of Reagan National Airport were briefly halted.

Most of the firing happened around US Navy Building 197, which employs 3,000, although more than 36,000 people work inside the complex.

Hundreds of police and other security personnel and several helicopters participated in the operation.

The shooting panicked local Muslims as since 9/11 suspects in such incidents have often been identified as people of Muslim origin.

Soon after the shooting, two US television channels – CBS and NBC – identified the dead gunman as Rollie Chance but later retracted the name.

President Obama, who was briefed several times about the unfolding situation by top White House counter-terrorism officials, said the authorities “still don’t know all the facts”.

“We’re confronting yet another mass shooting and today it happened on a military installation in our nation’s capital. It’s a shooting that targeted our military and civilian personnel,” he said.

“These are men and women who were going to work doing their jobs and protecting all of us,” the US president said. “They’re patriots. They know the dangers of serving abroad, but today they faced the unimaginable violence that they wouldn’t have expected here at home.”

Mr Obama said he had instructed his team to ensure that “the investigation (is) seamless, so that local and federal authorities are working together”.

Police said they were still trying to determine the motive behind the shooting.

The Navy Yard, created in 1799, was the world’s largest ordnance plant during World War II. Its military role has steadily diminished since then.