INTERNATIONAL FALLS (AP) - A fire that caused the collapse of a busy wooden railroad bridge near Minnesota's northern border has been ruled an accident.

Koochiching County Sheriff Perryn Hedlund says fire marshals found no evidence of foul play and believe the fire was started by a mechanical failure. He didn't want to speculate on what went wrong.

A Canadian National Railway engineer spotted the blaze early Wednesday. The collapse blocked a CN line from Prince Rupert, British Columbia, to Chicago. It crosses the border at Ranier, Minnesota, near International Falls. It's one of the busiest rail crossings on the border.

Railroad spokesman Brent Kossey says CN hopes to restore service in the coming days. In the meantime, it's rerouting traffic to maintain service to its customers.