A single gunshot fired at U.S. President Barack Obama's campaign field office in Denver Friday is being investigated by police.

The building was occupied when the shooting occurred, but no one was injured, said Detective Raquel Lopez, a representative of the Denver Police Department.

Lopez said police were called about the incident at 77 W. 9th Ave. around 3 p.m. local time (5 p.m. EDT). It is uncertain at this writing how many people were in the office when the shot was fired.

"It is an active investigation, and we are looking into all information coming in," Lopez said in a telephone interview.

Local media outlets reported that police have a description of a "possible vehicle of interest." Because the investigation is active, however, Lopez couldn't reveal more details.

Here's a photo of one result of the incident tweeted by Sam Levin, a reporter for the local alternative newspaper Westword.