Kamala Harris campaign office damaged by gunfire days ahead of scheduled rally

An office in Arizona used by Kamala Harris' campaign was shot at early Monday morning in the second apparent gun attack in a week, according to investigators.

Police in Tempe, Arizona, responded to the office, which the local Democratic Party also uses, after they received calls from staffers about the damage. At least five bullet holes were found in the windows and the door.

"No one was inside the office during the overnight hours, but this raises concerns about the safety of those who work in that building, as well as those nearby," Tempe Police spokesperson Sgt. Ryan Cook told ABC News.

Tempe police said they were analyzing evidence and were taking "additional measures" after the shooting "to ensure the safety of staff and others in the area." A motive for the shooting has not yet been determined and the investigation continues, according to the police.

The same office was shot at just a week prior, on Sept. 16, in an incident the police said appeared to involve a BB or pellet gun. That shooting also happened just after midnight and caused "criminal damage," according to the police.

Arizona Democratic Party Chair Yolanda Bejarano condemned the vandalism in a statement to ABC News Phoenix affiliate KNXV.

"It's extremely sad that the Arizona Democratic Party has become the target of violence — it's not who we are as Arizonans or Americans. We are working with law enforcement to ensure this threat is taken seriously and that our staff members are safe while they're at work," she said in a statement.

Law enforcement around the country is under heightened alert over an increase in political violence threats.

Harris is scheduled to visit Arizona on Friday.