NHTSA has determined that certain models of the Jeep Cherokee, Grand Cherokee and Jeep Liberty are more likely to catch fire after rear impact crash than similar vehicles such as the Chevrolet Blazer, Toyota 4Runner and Ford Explorer.
The expanded probe will now undergo an engineering analysis to determine if the vehicles are safe.
"NHTSA's assessment of the data collected during preliminary evaluation indicates that rear-impact-related tank failures and vehicle fires are more prevalent in the (Jeep Grand Cherokee) than in the non-Jeep peer vehicles," the government agency said.
The affected vehicles include: 1993-2001 Jeep Cherokees; 1993-2004 Jeep Grand Cherokees; and 2002-2007 Jeep Liberties.
At issue is the design of the vehicle, which places the fuel tank behind the rear axle. Chrysler Group LLC, which owns the Jeep brand, changed the design for 2005 models, but insists that the previous design remains safe.
In a statement this morning, the company said:
"The 1993-2004 Jeep Grand Cherokee and other subject vehicles meet or exceed all applicable federal motor vehicle safety standards and have excellent safety records with hundreds of billions of vehicle miles driven."
Additionally, Chrysler added, "We would expect that a similar analysis of subject vehicles recently added to this investigation would support a similar conclusion."
But not everyone agrees with Chrysler.
The Center for Auto Safety, a consumer group founded by Ralph Nader, says that the fire death rate in the Jeeps with the fuel tank behind the rear axle is 20 times higher than a Ford Explorer, which has the tank in front of the rear axle.
The group filed a petition with NHTSA to recall the Jeep Grand Cherokee in 2009, and it continues to monitor the issue.
In a November 2011 letter to Chrysler CEO Sergio Marchionne, Center for Auto Safety Executive Director Clarence Ditlow, compared the Jeeps to the notorious 1970s Ford Pinto.
"The tragic question is how many more fatal fire crashes will it take before Chrysler recalls this Pinto for soccer moms," he wrote.