Published: Dec 11, 2013 10:31 PM EST

WASHINGTON (AP) - Police and school officials say American University's campus in the nation's capital is on lockdown after police received calls about a man with a gun.

That report came in to Washington police about 7:40 p.m. Wednesday, but authorities say officers have not confirmed the report and so far, no gunman has been found.

The university sent tweets saying the campus was in lockdown. It urged students to shelter in place, adding in a tweet that authorities were continuing to search for a possible armed person.