WASHINGTON (Reuters) - Police briefly ordered a lockdown of the U.S. Capitol early on Friday as they sought to investigate a "suspicious item" that looked like a weapon inside the backpack of a congressional employee, law enforcement officials said.

The item was found to be "not a threat," U.S. Capitol Police later said in a statement.

One law enforcement official said the suspicious item turned out to be a power drill. The woman with the item was passing through the Rayburn House Office Building, which is adjacent to the Capitol and holds offices of members of the House of Representatives.

Police gave an all-clear notice to reopen the Capitol building shortly after 9:30 a.m., about a half an hour after the lockdown began.

The lockdown meant people in the Capitol and some nearby congressional buildings were required to remain in their offices with locked doors and windows. The U.S. Capitol visitor's center also was temporarily closed.

(Reporting by Richard Cowan, Emily Stephenson and David Morgan; Writing by David Alexander; Editing by Tim Ahmann and Chizu Nomiyama)