Senator Bernie Sanders’ Vermont office caught fire. Arson is suspected, but the motive is unclear.

Vermont police are searching for a suspect who allegedly started a fire Friday outside the office of US Senator Bernie Sanders. The small fire caused minor damage but no injuries.

Authorities say an unknown suspect sprayed what they described as a possible accelerant on the office door, set it on fire and fled. They said the suspect remained at large and no motive had been established.

“A significant fire engulfed the door and part of the lobby, preventing the exit of staff members who were working in the office and endangering their lives,” Burlington police said in a statement. “The sprinkler system was activated and largely extinguished the fire.”

Earlier in the day, the Burlington Fire Department said it responded to a call Friday morning and found a fire between the lobby, elevator and front door of Sanders’ third-floor office in Burlington. The office door sustained moderate fire damage and much of the third floor sustained significant water damage. Sanders’ offices and those nearby were evacuated.

A Sanders spokesperson did not immediately respond to a request for comment. Sanders was not in the office.