US safety regulators have opened a preliminary investigation of about 3-million older Jeep Grand Cherokees with fuel tanks that may present a fire risk in a crash.

The investigation was opened on Monday by the US National Highway Traffic Safety Administration. The action is short of a recall and a Chrysler spokesman said owners of the 1993-2004 model vehicles should take no action now.

Chrysler said it was co-operating with the NHTSA on the investigation. It said the Jeep Grand Cherokees from those model years "met or exceeded" federal safety standards.

In October 2009 the Centre for Auto Safety asked the NHTSA to open an investigation into the vehicles, saying records showed that from 1992 to 2008 the SUVs were involved in 172 fatal fire crashes with 254 deaths.

The centre did not say how many, if any, of the deaths were related to the fuel tanks.

The preliminary investigation comes as automakers face tougher scrutiny by safety regulators following Toyota's huge recalls that began late in 2009.

The Centre for Auto Safety, founded by Consumers Union and Ralph Nader in 1970 said the Grand Cherokee fuel tank storage system was defective and posed a hazard in a crash.

It said the Grand Cherokee's plastic fuel tank from those model years was behind the rear axle, extended below the rear bumper and had inadequate shielding, leaving it vulnerable to rupturing or leaking in a crash.

Chrysler put the fuel tank in front of the rear axle and shielded it from the 2005 model year, the centre said.

In response to the centre's request federal safety investigators carried out a preliminary examination of data that isolated 10 crashes with 13 fatalities most likely associated with the defect the center described.

The NHTSA said a preliminary review of data supplied to federal regulators did not find the Grand Cherokee "over-represented for post-crash fires".

"Further review and investigation into these incidents is needed to determine the existence of any relationship between the alleged defect and each fire or leak." - Reuters

Chrysler SA said it had sold about 2200 of the affected models in South Africa but was "not aware of any Jeep Grand Cherokee fuel tank problems relating to South African vehicles".