'Shots fired' at Obama campaign office

Staff were in the office when the incident occurred mid-afternoon. "It looks like it was one shot that was fired into the structure," said Denver police spokeswoman Raquel Lopez, cited by The Denver Post.

A photo posted online by the Denver Westword showed a window broken at the front of the office. Police were searching for a "possible vehicle of interest," said Lopez, giving no further details.

Obama campaign officials did not immediately comment on the incident, which comes as Obama and Republican rival Mitt Romney battle into the final weeks before the November 6 presidential election.