BILLINGS, Mont. — U.S. railroads forced to turn over details of their volatile crude oil shipments are asking states to sign agreements not to disclose the information. But some states are refusing, saying Thursday that the information shouldn’t be kept from the public.

Federal officials last month ordered railroads to make the disclosures after a string of fiery tank-car accidents in North Dakota, Alabama, Virginia and Quebec, where 47 people died when a runaway oil train exploded in the town of Lac-Megantic.