The White House briefing room and parts of two U.S. Senate office buildings were briefly evacuated within hours of each other on Tuesday after separate bomb threats, but it was not clear if the incidents were linked.

In a rare interruption of the White House daily press briefing, reporters were hustled out of the room for about 30 minutes after a bomb threat was phoned in to local police.

The Secret Service and bomb-sniffing dogs searched the premises and eventually gave the all-clear to resume the briefing by White House spokesman Josh Earnest.

President Barack Obama was in the Oval Office, just steps from the briefing room, and was not evacuated, Earnest said. First lady Michelle Obama and their two daughters were nearby in the White House residence and also were not moved.

"Evacuation was limited to the WH Briefing Room due to the specific nature of the threat, "Secret Service spokesman Brian Leary said in a statement on Tuesday night.

The immediate blocks around the White House, including Lafayette Square across Pennsylvania Avenue, were roped off and closed to tourists briefly, a Reuters witness said.

Hours earlier on Tuesday, authorities investigated reports of suspicious packages and a telephoned bomb threat at two U.S. Senate buildings and found nothing hazardous.

U.S. Capitol police cleared a room in the Dirksen building and the courtyard of the Russell building, which house U.S. senators and their staffs near the U.S. Capitol, and found nothing problematic.

"Because of the ongoing investigation the USSS cannot discuss any potential connection to the earlier threat at the U.S. Capitol," Leary said.