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The Republican campaign headquarters was firebombed in Hillsborough, North Carolina, on Saturday night, police said.

A flammable liquid was tossed through the front window of the office, setting the interior on fire temporarily and damaging furniture, the Hillsborough Police Department said in a statement.

"The flammable substance appears to have ignited inside the building, burned some furniture, and damaged the building’s interior before going out," police said. "The substance was housed in a bottle thrown through one of the building’s front windows."

Vandals also spray-painted a building next door with a swastika and the words "Nazi Republicans get out of town or else."

No one was in the building at the time, and police are investigating the act as vandalism and "hate graffiti."

Hillary Clinton issued a statement on Twitter Sunday calling the attack "horrific and unacceptable."