U.S. 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 regulators' website showed on Tuesday.

The investigation was opened on Monday by the U.S. National Highway Traffic Safety Administration. The action is short of a recall, and a Chrysler spokesman said owners of the 1993-2004 model year vehicles should take no action at this time.

Chrysler said it was cooperating fully with NHTSA on the investigation. It said the Jeep Grand Cherokees from those model years meet or exceed federal safety standards.

The Center for Auto Safety last October petitioned NHTSA to open an investigation into the vehicles, saying NHTSA records show that from 1992 to 2008 the SUVs were involved in 172 fatal fire crashes with 254 deaths.

The petition 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 Motor Corp's massive recalls starting in fall 2009.

The Center for Auto Safety, founded by Consumers Union and Ralph Nader in 1970, asked regulators to open an investigation in October 2009, contending that the Grand Cherokee fuel tank storage system was defective and posed a hazard in a crash.

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, the center said.

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

In response to the center's petition, federal safety investigators performed a preliminary examination of data that isolated 10 crashes with 13 fatalities most likely associated with the defect the center described, NHTSA said.

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

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, NHTSA said.

(Reporting by David Bailey and Bernie Woodall, editing by Gerald E. McCormick and John Wallace)

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