The U.S. rail safety regulator issued rules on Friday meant to prevent the kind of runaway fuel-train accident that devastated Lac-Mégantic, Que., last month.

Under the rules, rail cars carrying hazardous materials like combustibles may not be left unattended on main tracks or adjacent tracks unless specifically authorized.

Railroads must boost their safety procedures and record-keeping for trains that carry hazardous material and are braked, according to the rules from the Federal Railroad Administration.

Last month, a parked train carrying crude oil broke loose and crashed in Lac-Mégantic, exploding into a fireball that killed 47 people. It was North America's worst rail disaster in two decades.

"Safety is our top priority," U.S. Transportation Secretary Anthony Foxx said in a statement.

"While we wait for the full investigation [of the Canadian incident] to conclude, the department is taking steps today to help prevent a similar incident from occurring in the United States."

A release from the regulator specifically mentions the Lac-Mégantic derailment and says the FRA announcement "was made in response" to that incident.

With files from CBC News