One man was shot and a woman was stabbed at Washington DC's Union Station as the country was commemorating the 14th anniversary of the 9/11 terrorist attacks, according to police.
The stabbing and shooting happened early on Friday and were isolated incidents, Xinhua quoted police source as saying.
The woman was stabbed by the man when she was in the passageway connected to the train station. A security for the Securities and Exchange Commission, located next door to the station, then chased the perpetrator before the man turned on him with a knife.
The guard fired one shot at the man in the leg, according to police.
"We believe this is a domestic-related incident," said Metropolitan Police Department's Jeff Brown, adding "Obviously with this being 9/11, fears were heightened."
Security was revved up nationwide on Friday as the country was commemorating the 14th anniversary of the 9/11 terrorist attacks on the World Trade Centre in New York city and the Pentagon in Virginia.
