PORTLAND, Ore. (AP) — Oregon transportation officials are asking federal rail authorities to suspend crude oil trains in the Pacific Northwest's Columbia River Gorge until there is a better understanding of what caused a fiery derailment there this month.

State Department of Transportation officials presented their concerns Thursday at a meeting in Hood River and made public a letter to the Federal Rail Administration asking for the moratorium on oil-only trains in Oregon. The letter expresses concern about lag bolts, a type of fastener used on a curved section of track to attach the rail to the rail tie.

Union Pacific has said a failure of the bolts caused the June 3 derailment. More than 12 of the 96 oil cars derailed, sparking a fire and forcing evacuations. No one was injured.