WASHINGTON (CNN) -- The U.S. Coast Guard promised a "thorough review" after a training incident Friday along the Potomac River briefly triggered concerns about the security of the president on the anniversary of the Sept. 11 attacks.
"We are still gathering information (on) how this training event might have been misconstrued as an actual incident," the Coast Guard said in a statement.
Federal agency emergency operations centers were not aware of or notified about the exercise, and began implementing response procedures, a federal source told CNN.
A high-ranking Coast Guard official with detailed knowledge of the exercise told CNN that it was not considered a major exercise that would involve other agencies, so they had not been notified.
The training incident took place as President Obama was traveling across the Memorial Bridge following an event at the Pentagon shortly before 10 a.m. ET. CNN personnel saw what appeared to be a Coast Guard vessel working to prevent a boat from trying to enter a security zone.
Minutes later, there were reports on police scanners that the Coast Guard fired 10 rounds of ammunition.
A Department of Homeland Security representative later told CNN no shots of any kind had been fired.
"Reports in the media were based on overheard radio calls made over a training frequency," the Coast Guard said in its statement.
The Secret Service said Obama was back at the White House by the time of the reports of shots fired.
"I am extremely concerned about the report of a Coast Guard training exercise being conducted on the Potomac River as September 11 memorial ceremonies were in progress nearby at the Pentagon.
The anxiety caused by this situation on such a solemn day is extremely disturbing. I look forward to hearing from Secretary Napolitano about the decision-making process leading up to today's events. It sounds very much like the left hand didn't know what the right hand was doing."