WASHINGTON - As Toyota Motor Corp. expanded by 1.1 million vehicles a recall related to accelerator pedals, details emerged about the unusual steps U.S. officials took to urge Toyota to quickly address escalating safety and quality concerns, reported The Detroit News.

The expansion broadens Toyota's largest-ever recall and comes one day after the Japanese automaker said it would stop selling eight models involved in a separate accelerator pedal recall until it comes up with a fix for that problem. That affects production at six North American assembly plants. The eight models account for 60 percent of Toyota's U.S. sales volume.

The 1.1 million vehicle expansion involves Toyota's recall last fall of 4.26 million vehicles and comes as the National Highway Traffic Safety Administration was preparing to open a broader investigation into the central issue of that recall: whether unintended acceleration in several crashes was caused by the gas pedal being trapped by a floor mat.

The new vehicles being recalled under the action announced in September are 2008-2010 Highlander sport utility vehicles, 2009-2010 Corolla sedans, 2009-2010 Venza crossovers, 2009-2010 Matrix hatchbacks and 2009-2010 Pontiac Vibe hatchbacks; the Vibe was jointly engineered by Toyota and General Motors Co. Toyota disclosed the move in a two-page letter to NHTSA that was reviewed by The Detroit News.

The increase means Toyota has recalled 5.35 million vehicles in the probe linked to pedal entrapment by floor mats. Toyota in November agreed to repair or replace the pedals, replace the floor mats, and in some cases modify software that controls the throttle and reshape the floor surface.