US federal authorities are investigating fires at two polling stations reported Monday morning in the Portland, Oregon area and Vancouver, Washington.

Specifically, police responded to a call about a fire in Portland at about 3:30 a.m. Monday, the Portland Police Bureau said. An “incendiary device” was placed inside the box and security personnel extinguished the fire, officials said.

Federal officials are investigating the incident in Portland, as well as a second fire in nearby Vancouver, Washington, with the help of state and local authorities, said Steve Byrd, a spokesman for the FBI’s Seattle office.

In a latest development, police have announced that a “suspicious vehicle” has been located in connection with the fires which appear to be linked.

CCTV captured a Volvo pulling up to a drop box in Portland, Oregon, shortly before security personnel discovered the fire inside the box on Monday, Portland Police Bureau spokesman Mike Benner said at a news conference.

That fire destroyed three ballots, while a fire at a polling station in nearby Vancouver, Washington, early Monday destroyed hundreds of ballots. The devices were attached to the outside of the boxes, police said.

Authorities said at a press conference in Portland that enough material was recovered from the incendiary devices to show that the two fires are connected, but also to an incident on Oct. 8, when an incendiary device was placed in a different ballot box in Vancouver.