A report of shots fired early Thursday at the same Washington Navy Yard where a gunman killed 12 people in 2013 prompted a massive police response and lockdown, but after an extensive search, authorities issued an 'all clear' at the facility.
The US Navy also confirmed there was no sign of a shooting. "All personnel OK," the Navy said in a tweet. "Follow-on NCIS investigation ongoing."
The facility where the shots were first reported was largely emptied Thursday as civilian and military law enforcement officers swept through.
Navy Commander Scott Williams, who was at the Navy Yard on Thursday morning and also during the attack two years ago, initially told CNN's "New Day" that the scene unfolding around the complex was "pretty much a mirror image of 2013". This turned out to be untrue.
The apparent false alarm is a sign of the tension in the US as the July 4 weekend approaches, after ISIS spokesman Abu Muhammad al-Adnani recently said that jihadists should make Ramadan a time of "calamity for the infidels ... Shi'ites and apostate Muslims."
"Muslims everywhere, we congratulate you over the arrival of the holy month," he said. "Be keen to conquer in this holy month and to become exposed to martyrdom.