**Reports of a shooting incident on the Potomac river just outside Washington DC were a training exercise, US officials say.**CNN had reported that 10 rounds were fired as a vessel tried to go through a security zone.
But officials later said the incident had been a training exercise and no shots were fired.
The incident came as ceremonies marking the anniversary of the attacks of 11 September 2001 were being held.
CNN played an audiotape of the Coast Guard saying: “If you don’t slow down, your vessel will be fired upon.”
The Department of Homeland Security later confirmed that the reported incident was a training exercise, and that no shots were fired.
Remembrance services were held across the US on the eighth anniversary of the 11 September 2001 attacks.
Nearly 3,000 people died when the four planes crashed in New York, at the Pentagon and in a Pennsylvania field.
Tributes
Speaking at the Pentagon, President Barack Obama paid tribute to the victims, saying the years would not diminish the loss of that day, and vowed to “never falter” in pursuit of al-Qaeda.
Meanwhile, thousands gathered for ceremonies in a square near New York’s Ground Zero.
Remembrance services are being held around the country, with moments of silence being observed at the three sites.
Americans have also been encouraged to contribute to a national day of community service.