The Capitol tightened security Monday in response to the possibility that suspects from Monday morning's fatal shootings at Washington's Navy Yard are still at large, with the Senate in partial lockdown for part of the afternoon.

Senate Sergeant at Arms Terrance Gainer announced in the late afternoon that only staff would be allowed to enter the Senate side of the building and its adjacent office buildings. That followed a period of about an hour when no one was allowed to enter or leave the Senate complex.

The rest of the Capitol complex, including the House side and the visitor's center, remain open.

Gainer said in a prepared statement that while there is no information to suggest anyone inside the Capitol is in danger, "out of an abundance of caution, we feel this is the best course of action to keep everyone safe."

Earlier in the afternoon, Senate Majority Leader Harry Reid adjourned the chamber until Tuesday in response to the fatal shootings, in which 12 people plus the shooter were killed.

The Nevada Democrat announced his decision on the chamber floor immediately following Senate Chaplin Barry Black's opening prayer. Reid said the day's business, which included debate on an energy saving bill and votes on two judicial nominees, would be rescheduled at a time to be determined later.