By Colleen Jenkins

WINSTON-SALEM, N.C. (Reuters) – Police in North Carolina sought leads on Monday about a fire they said was deliberately set at a local Republican headquarters over the weekend and a graffiti message warning the political party to “leave town or else.”

Investigators are treating the incident as arson. The fire caused heavy damage to the Orange County Republican Party’s office in Hillsborough, North Carolina, located about 40 miles from the state capital of Raleigh. No arrests have been made.

“This is political terrorism,” Dallas Woodhouse, executive director of the North Carolina Republican Party, said in a phone interview.

The crime occurred less than a month before the Nov. 8 election. Both Republican presidential nominee Donald Trump and Democratic rival Hillary Clinton condemned the attack. North Carolina is considered a battleground state that could play a pivotal role in the presidential contest.

“We are taking this incident very seriously and have significant resources at the local, state and federal level committed to this investigation,” Hillsborough Police Chief Duane Hampton said in a statement on Monday, asking anyone with information to come forward.

Hillsborough police said a bottle containing flammable material ignited after being thrown through a front window of the headquarters between midnight and about 9 a.m. on Sunday, when a nearby business owner reported the crime.

“Someone has firebombed through the window (of) the Republican party up here beside me and sprayed all over the side of my building, ‘Nazi Republicans leave town or else,'” the caller told a 911 operator in a call released on Monday.

A swastika also was spray-painted on the neighboring building, police said. They said no one was in the party office at the time, but the substance burned furniture and charred campaign signs.

White House spokesman Josh Earnest praised the efforts of self-described Democrats who raised about $13,000 in an online GoFundMe campaign to help Republicans reopen the office.

“That’s consistent with the values that we lift up in this country,” he said at a news briefing on Monday. “There is no justification for the use of violence to advance a political agenda.”

In a tweet on Sunday, Clinton said she was grateful no one was hurt in the attack, which she called “horrific and unacceptable.”

Trump blamed his Democratic opponent’s supporters for the crime.

“Animals representing Hillary Clinton and Dems in North Carolina just firebombed our office in Orange County because we are winning,” he said on Twitter.

Registered Democrats far outnumber Republicans in Orange County, according to elections board data. President Barack Obama won 70 percent of the vote there in the 2012 presidential election.

Despite those statistics and the divisive nature of this year’s presidential race, local Republicans said the incident took them by surprise.

They remained undeterred, however, starting the clean-up at their strip-mall headquarters and getting back to work on Monday in a bus being used as a mobile office.

“We’re not going to be intimated, we’re not going to be cowed,” Woodhouse said.

(Additional reporting by Doina Chiacu in Washington; Editing by G Crosse and Leslie Adler)

Photo: Evelyn Poole-Kober views the damage caused in a firebomb attack on local offices of the North Carolina Republican Party in Hillsborough, North Carolina, U.S. October 17, 2016. REUTERS/Chris Keane