The Cannon House office building in Washington was briefly evacuated on Thursday after a fire alarm went off just before noon.
After looking into what had happened, US Capitol Police and the Architect of the Capitol found "a malfunctioning electrical panel," Capitol Police spokeswoman Eva Malecki said in a statement. She added that there were "no reports of smoke or fire."
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People were allowed back into the building, which is part of the US Capitol complex, at 1 p.m. ET, according to the statement.
After the evacuation, Capitol Police initially closed off the block surrounding the building, while dozens of construction workers doing work on the building waited outside.
Two fire trucks arrived at the building after the alarm went off but departed soon afterward.
Some lawmakers with offices in the building tweeted about the evacuation. Rep Dan Kildee, a Michigan Democrat, and Rep. Mike Johnson, a Louisiana Republican, both said on Twitter that members of their staffs were safe.
The House and Senate are out of session until the November midterm elections, and many lawmakers are back in their home states or congressional districts.
The incident took place a day after authorities intercepted a series of potential explosive devices targeting Democrats, including former President Barack Obama and 2016 Democratic presidential nominee Hillary Clinton.
Democratic Rep. Maxine Waters of California was one of the apparent targets. Two sources told CNN she was the intended recipient of a suspicious package intercepted at a congressional mail facility outside of Washington.
There appears to be no connection between those events and the evacuation of the House office building on Thursday.