The U.S. Capitol was briefly evacuated Wednesday evening after police said they were tracking an aircraft “that poses a probable threat,” but the plane turned out to be a military aircraft with people parachuting out of it for a demonstration, officials told The Associated Press.

The alert was sent to congressional staffers Wednesday evening after police said they were “tracking an aircraft that poses a probable threat.” 

According to Politico, a military parachute demonstration for Military appreciation night at Nationals Park and an apparent lack of communication with Capitol police led to the warning.

The aircraft, a single-engine plane, was reported to be circling around Washington after taking off from Joint Base Andrews in Maryland, two people familiar with the matter. The people said the aircraft did not report taking off and did not have appropriate clearance. The people were not authorized to discuss the matter publicly and spoke to The Associated Press on condition of anonymity.

Nationals Park is a little more than a mile away from the U.S. Capitol.