NAGOYA (Kyodo) U.S. authorities are urging Toyota Motor Corp. to issue a mandatory recall over loose floor mats in some of its cars, stepping up the pressure for the Japanese automaker to admit that the vehicles in question have a safety defect, sources said Friday.

Earlier this month, Toyota issued a "safety recall" for 3.8 million vehicles in seven models, including the Prius hybrid and Lexus cars, warning that an unsecured driver-side floor mat could slip forward and jam the accelerator pedal.

Toyota President Akio Toyoda also expressed regret for the deaths of four people in a fatal crash in August involving a Lexus ES350 in San Diego that is suspected of being linked to the problems with the floor mat.

But in a recent letter to the National Highway Traffic Safety Administration, Toyota emphasized it "has not determined that the vehicles contain a 'safety-related' defect" as it is apparently hoping to keep the situation under control with voluntary measures, the sources said.