Hillsborough police are investigating the apparent weekend firebombing of the Orange County Republican headquarters, an incident that one GOP official called an act of "political terrorism."

Police say the incident occurred when a bottle of flammable liquid was thrown through the front window of the office on Ja-Max Drive.

The words, "Nazi Republicans get out of town or else" were spray painted on the side of an adjacent building.

"This highly disturbing act goes far beyond vandalizing property; it willfully threatens our community's safety via fire, and its hateful message undermines decency, respect and integrity in civic participation," Hillsborough Mayor Tom Stevens said in a statement. "Acts like this have no place in our community."

Orange County, home to the University of North Carolina in nearby Chapel Hill, is overwhelmingly Democratic. Democrats and independents outnumber Republicans 5-1.

Hillsborough police and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were continuing to investigate.

Dallas Woodhouse, executive director of the state GOP, called the bombing "political terrorism."

"The office itself is a total loss," he said. "The only thing important to us is that nobody was killed, and they very well could have been."

Later, Woodhouse said, "Whether you are Republican, Democrat or Independent, all Americans should be outraged by this hate-filled and violent attack against our democracy. … Everyone in this country should be free to express their political viewpoints without fear for their own safety."

The incident comes barely three weeks before an election marked by heightened tensions and passion on both sides.

On Sunday the Bangor Daily News reported that about 20 cars were vandalized with spray paint outside a Saturday rally for GOP presidential candidate Donald Trump.

Earlier this year violence broke out with protesters at a Trump rally in Chicago. And one protester was sucker-punched at a Trump rally in Fayetteville.

"You hope (the firebombing) is an isolated incident," said Ferrel Guillory, a political analyst at UNC Chapel Hill. "It always happens that toward the end of the campaign, emotions get both frayed and intensified."

N.C. Democratic Party Chair Patsy Keever called the bombing "outrageous."

"The North Carolina Democratic Party strongly condemns this attack. Violence has no place in our political system," she said. "We hope the perpetrators of this attack are brought to swift justice, and we are thankful that no one was hurt. Our deepest sympathies are with everyone at the North Carolina Republican Party."

Democrat Hillary Clinton's N.C. campaign tweeted, "Thinking of everyone at the @NCGOP after the horrific and unacceptable attack on the Orange County HQ. Grateful all are safe."

In the meantime, Woodhouse said he's sending an advisory to county Republican offices across the state warning them to take extra caution.

Anyone with information is asked to call the police department's tip line at 919-732-3975.