A model poses next to a Jeep Cherokee during the press preview day of the North American International Auto Show in Detroit, Michigan, US on?January 14, 2014.?[Photo/Agencies]

Federal safety regulators have upgraded an investigation of sun visor-related fires in recent-model Jeep Grand Cherokee and Dodge Durango SUVs.

The US National Highway Traffic Safety Administration said Tuesday it had opened an engineering analysis into nearly 600,000 Grand Cherokees and Durangos, from model years 2011 through 2013, because a potential short circuit could cause a fire near the sun visors of those vehicles.

An engineering analysis is the final step before NHTSA determines if the vehicles should be recalled.

NHTSA's Office of Defects Investigation said it had reports of five fires in those vehicles, and the manufacturer had reported 40 incidents, resulting in three alleged injuries.

Chrysler Group, a unit of Italy's Fiat SpA, said in a statement Tuesday its engineers continued to investigate the issue while "fully supporting" the NHTSA probe.

The reported incidents range from minor overheating to an open flame, the NHTSA said.

In some reports, "the fire spread to the front seats and/or door panels of the vehicle," the agency said. In another, the sunroof was damaged and the glass shattered.

The fires appeared to be caused by an electrical short in the sun visors' lighted vanity mirrors, the NHTSA said.