Loud noise heard near White House

A loud noise was heard at the White House this morning just before US President Barack Obama was due to leave for Selma in Alabama, following which the Secret Service locked the press room.
The press room was unlocked for a brief moment, as the situation inside White House remained unclear.
The loud noise was heard as the media gathered outside near the South Lawn for the departure of Obama and the First Family on the way to Selma, Alabama, for a historic 50th anniversary march.
Secret Service then moved press back into the briefing room and locked the doors. The press room was unlocked some 10 minutes later.

"It's not over but the door's unlocked," a Secret Service official said. The press room was locked again a few minutes later.
There was a high-level of consternation among Secret Service walking outside. On Twitter photos appeared of a fire at a nearby souvenir stand. It was not clear if this was the cause of lockdown.