DETROIT (AP) — U.S. safety investigators are looking into complaints of fires that may have been caused by the seat belts in Ford F-150 pickup trucks.

The investigation covers trucks from the 2015 through 2018. Ford sold about 2 million F-150s during those years.

The National Highway Traffic Safety Administration is investigating five complaints that fires began in the trucks after seat belt pretensioners made by ZF-TRW or Takata were activated. Pretensioners prepare seat belts to gradually restrain passengers. Three fires destroyed the trucks, while two went out by themselves.

The agency says the fires began in a support pillar that houses the belts. Investigators will figure out the exact cause and whether a recall is necessary. None of those who complained reported any injuries.

Ford says it's cooperating with the probe.

In one of the complaints, an owner in Grand Rapids, Michigan, told NHTSA that on July 7, a deer ran into the driver's side of a pickup, causing minor damage. The side air bags inflated, and after five to 10 minutes, a passenger noticed a fire on the bottom of the post between the front and rear doors where the seat belts are located. "The truck went up in complete flames in a matter of minutes and is a complete loss," the owner wrote.

People who file complaints are not identified in the NHTSA database.

Messages were left Tuesday seeking comment from ZF-TRW and Takata.