White House press secretary Robert Gibbs trounced CNN for erroneously reporting that shots were fired during a Coast Guard exercise on the Potomac River Friday morning, saying the reports, not the military exercise, caused unnecessary panic. Gibbs said he wouldn’t second-guess the Coast Guard’s decision to hold a training exercise on the anniversary of the September 11 attacks, which briefly shut down departing flights from Washington National Airport. He added that the Coast Guard was holding a news conference to explain the exercise. "Hopefully CNN will go,” Gibbs said. "My only caution would be that before we report things like this, checking would be good." He later got into a tense exchange with CNN reporter Elaine Quijano. The Coast Guard said they simulated the sound of gunfire on an open police-radio frequency, but that no shots were fired. Neither the White House, the Coast Guard, nor CNN has apologized for the snafu, which is being compared to the New York photo-op flyover that set off a panic in April.