The United States Capitol Police (USCP) announced an "active bomb threat" Thursday morning near the Library of Congress, locking down or evacuated portions of the Capitol Building.
A Fox News report quoted a Republican source as saying that Capitol Police warned members of Congress about a man in the area, "claiming to have explosives in his truck."
A negotiator has reportedly been sent to the scene with the FBI responding to the developing situation.
The USCP urged civilians to stay away from the area in a message tweeted at 9:40am local time.
AP reporter Mike Balsamo said officials were "trying to determine whether the suspicious device in the pickup truck is an operable explosive and whether the man in the truck was holding a detonator."
While Fox later reported the Capitol has not been placed on lockdown, it said residents of nearby buildings were being asked to evacuate.