The Coast Guard was conducting a training exercise in the Potomac River moments before President Barack Obama crossed a nearby bridge for a Sept. 11 commemoration.
Coast Guard Chief Keith Moore said Friday no shots were fired as part of the exercise, although media reports suggested shots had been fired in the river. News stations showed video of Coast Guard vessels in the water.
Departures from Reagan National Airport were halted shortly after 10 a.m. as a precaution, Federal Aviation Administration spokeswoman Diane Spitaliere said. The airport borders the Potomac River near where shots were reported fired.
Obama had traveled to the Pentagon for a ceremony marking the eighth anniversary of the Sept. 11 terrorist attacks.