HILLSBOROUGH, N.C. -- Mike Pence toured the site of an apparent arson attack and graffiti vandalism at a county Republican Party headquarters in North Carolina today, calling it "an act of political terrorism."

"An attack on our political system is an attack on us all," the Republican vice-presidential candidate told reporters after touring the inside of the torched office.

"Everyone ... Republicans, Democrats or independents, universally condemn this attack," he said. "And we would urge anyone that might have information who perpetrated this attack to come forward and share that information with the proper authorities so we can bring to justice those individuals that were responsible for what occurred here."

The suspected firebombing at the GOP's Orange County office in Hillsborough happened early Sunday morning, police believe. Police said "a bottle containing flammable material was thrown through a front window" of the GOP office, damaging the inside and some furniture "before going out on its own." Graffiti was spray-painted on the side of a building next door. No one was injured.

As Pence spoke to reporters this afternoon, he would not say if he agrees with running mate Donald Trump that polling places are going to be "rigged." He said the point Trump had made was that there is "overwhelming bias in the media" and said the torched office was evidence of that.

"This has gotten very little national media attention," Pence said. "And I can't help but feel that had this been the other way around, had it been an attack on this country on the other political parties county headquarters, that the level of national media coverage and the discussion would be significantly different and I think most of the American people know that."

He added there had indeed been "proven instances of voter fraud" and urged people to get involved at polling places.

As the investigation into the apparent arson attack continues, Hillsborough police said Monday they are working with the federal and state bureaus of investigation, the Bureau of Alcohol, Tobacco, Firearms and Explosives and the Orange County Sheriff's Office. The Secret Service also is supporting the investigation, police said.

A law enforcement source told ABC News that evidence has been sent to the FBI laboratory in Quantico, Virginia, for analysis.