By Colleen Jenkins
WINSTON-SALEM, N.C. (Reuters) - Police in North Carolina sought leads on Monday about a fire they believe 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, about 40 miles (65 km) from the state capital of Raleigh.
"This is political terrorism," said Dallas Woodhouse, executive director of the North Carolina Republican Party.
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 Nov. 8 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. "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.
Republicans said the incident took them by surprise but left them undeterred as they started clean-up efforts at their strip-mall headquarters and worked in a bus being used as a temporary mobile office.
"We're not going to be intimated; we're not going to be cowed," Woodhouse said.
On Monday, the Arizona Republican Party headquarters in Phoenix was evacuated for about two hours after a bomb threat was left by phone. Police said nothing was found during a search of the premises.
Party officials said the call was received from an adult male at about 3:15 p.m. local time saying there was a bomb in the building and for occupants to get out.
(Additional reporting by Doina Chiacu in Washington and David Schwartz in Phoenix; Editing by Dan Whitcomb and Lisa Shumaker)