The US Coast Guard has caused alarm in Washington DC by holding a training exercise in the Potomac River moments before President Obama and his motorcade crossed a nearby bridge.
Initial media reports suggested the Coast Guard fired 10 rounds on a recreational boat.
However spokesman Keith Moore said no shots were fired as part of the exercise.
The incident occurred as Americans mourned today's eighth anniversary of the September 11 attacks on the Pentagon and the World Trade Center in New York.
President Barack Obama visited the city's Pentagon memorial and met with loved ones of those who died.