US safety regulators said on Tuesday they have opened an investigation into 450,000 Dodge Durango sport utility vehicles made by DaimlerChrysler's Chrysler arm and have upgraded an investigation into 217,000 Chrysler cars, Reuters reported.

According to Reuters, the National Highway Traffic Safety Administration opened the Durango probe last Thursday after receiving four complaints that the upper ball joint in the front suspension could fail, causing the driver to lose control. In two complaints, the wheel separated; in the other two, the suspension collapsed, the report said.

NHTSA also said it had 81 complaints that the ball joints wore out prematurely and the investigation covers 1998 to 2003 Durangos, Reuters added.

The news agency said the upgraded investigation, known as an engineering analysis and usually the last step before a recall, involves problems with the interlock between the ignition and the transmission on 1999 Plymouth Breeze and Dodge Stratus cars and Chrysler Sebring convertibles.

According to Reuters, NHTSA said it had found 113 complaints where the key could be removed from the ignition without the transmission in park, or where the transmission could be shifted out of park with the ignition off, both of which led to the vehicles rolling unexpectedly. The complaints include reports of 28 accidents and five minor injures, Reuters added.