No one was injured when a rock shattered a window of presidential candidate Ron Paul's Washington state campaign headquarters in Bellevue, the campaign reported.

Two volunteers sitting by the window felt the wind and glass when the rock broke the window around 6 p.m. on Sunday, Jan. 29, and the King County campaign coordinator ran outside and saw a gray vehicle driving west on Northeast 20th Street in Bellevue, according to the campaign press release on the incident. Bellevue Police responded to the incident, the campaign reported.

“This is a regrettable incident. We’d much prefer that people air their grievances in a battle of ideas rather than through violence,” said Ron Paul 2012 National Campaign Chairman Jesse Benton.    

Washington State Director Alexander Skouras said in a prepared statement: "After the incident, the volunteers immediately returned back to their work to help Restore America Now."

Paul, the congressman from Texas' 14th Congressional District, is expected to face off with former Massachusetts Gov. Mitt Romney, former Speaker of the House Newt Gingrich of Georgia and former Pennsylvania Sen. Rick Santorum in Washington state Republican caucuses, which are set for March 3.