Authorities ordered hundreds of cancer-stricken children and their supporters to leave a park by the White House this weekend, citing security concerns as the president was scheduled to head to a speaking engagement.

The Washington Post reports that the Secret Service ordered Lafayette Square cleared Saturday night as a vigil was about to begin during the two-day CureFest for Childhood Cancer.

U.S. Park Police spokeswoman Sgt. Anna Rose says the Secret Service announced the security closure for presidential movement at 7:15 p.m. President Barack Obama spoke later that night at the Congressional Black Caucus Foundation's annual awards dinner Saturday night.

In a statement, Secret Service spokesman Brian Leary says that the closures were part of standard protocols near the White House, but that the agency regrets not communicating the timeline more effectively to those involved in CureFest.

Event organizers say the closure dragged on for at least two hours and some sick children had to return to hotel rooms.