Washington, Oct 13 (IANS): A drive-by shooting occurred Friday afternoon at US President Barack Obama's campaign office at downtown Denver, police said.

One shot was fired, shattering the street-front window of the Democratic campaign headquarters office, but no one was injured, according to police spokeswoman Raquel Lopez who said a number of people were working inside at the time of the shooting.

Police arrived on the scene within minutes and finished their onsite investigation in two hours, reported Xinhua.

"At this point, we're not saying it was politically motivated. We're looking at all motives," Lopez said, adding that surveillance video taken at the scene was being reviewed.

The presidential race in Colorado is extremely close, with a Quinnipiac/CBS/NYTimes poll released Thursday showing Republican challenger Mitt Romney overtaking the president 48 percent to 47 percent. Last month, the same poll gave Obama a 48-47 advantage.

Last week, just a few miles away at the University of Denver, Obama and Romney squared off in the first of three presidential debates, with survey results showing Romney winning that exchange by a 72-16 percent margin.

Colorado is one of several hotly contested "battleground" states, where the candidates are neck and neck, according to polls. These states will likely decide the Nov 6 election.