U.S. safety regulators upgraded a probe of about 480,000 Ford Motor Co sedans to examine floor mats that may interfere with the accelerator pedal, according to documents filed on Friday.

In 2008-2010 Ford Fusion, Mercury Milan and Lincoln MKZ sedans, unsecured or double stacked floor mats under the driver's foot well may block the accelerator pedal from returning to idle.

The National Highway Traffic Safety Administration said it upgraded its investigation to an engineering analysis to further assess the scope of the problem.

(Reporting By Deepa Seetharaman)