Federal safety regulators have sharply rebuked Toyota Motor Corp. for issuing 'inaccurate and misleading' statements asserting that no defect exists in the 3.8 million vehicles it recalled after a Lexus sedan accelerated out of control in San Diego County, killing four people. The National Highway Traffic Safety Administration issued a statement Wednesday that the recalled Toyota and Lexus vehicles do have an 'underlying defect' that involves the design of the accelerator pedal and the driver's footwell. Toyota officials have said they believe the Aug. 28 accident, and other uncontrolled-acceleration incidents across the country, occurred after the gas pedal became entrapped in an improperly installed floor mat. In formal recall notices being mailed out this week, Toyota asks customers to remove the driver's side mats. Separately, the company issued a statement Monday saying its recall letter 'confirms that no defect exists in vehicles in which the driver's floor mat is compatible with the vehicle and properly secured.' Toyota also posted a video statement disputing news reports that problems of unintended acceleration may be related to other factors, such as electronic throttle control systems. That prompted NHTSA to issue a clarification. 'Safety is the No. 1 priority for NHTSA and this is why officials are working with Toyota to find the right way to fix this very dangerous problem,' the statement said. 'This matter is not closed until Toyota has effectively addressed the defect by providing a suitable vehicle-based solution.' The statement is an unusual public upbraiding of an automaker by the regulatory agency, according to auto safety experts, and threatens to dent Toyota's credibility just as it seeks to assure customers that its vehicles are safe. 'This is particularly public at a particularly difficult time for Toyota,' said Sean Kane, chief of Safety Research & Strategies, a Rehoboth, Mass., consulting firm. 'Toyota was trying to say it has a clean bill of health from NHTSA, when it does not.' In response to NHTSA's statement, Toyota said it was 'never our intention to mislead or provide inaccurate information.' The statment added that it was still developing 'vehicle-based' remedies to prevent unintended acceleration events, in which motorists say their vehicles suddenly speed out of control. Toyota spokesman Brian Lyons suggested last month that these remedies might include physical changes to the placement of the pedals, or a change to the engine control software in the vehicles' onboard computers. On Wednesday, however, Lyons declined to comment on any specific fixes. Toyota announced the voluntary recall Sept. 29, one month after a 2009 Lexus ES 350 sped out of control on a suburban San Diego highway, killing California Highway Patrol officer Mark Saylor, his wife, Cleofe Lastrella, their 13-year-old daughter Mahala and Chris Lastrella, Cleofe's brother. The incident drew widespread public attention because the final moments were captured as Chris Lastrella made a frantic 911 call describing Saylor's futile efforts to stop the car, which crashed through an embankment and burned. The accident and recall prompted Toyota President Akio Toyoda to express remorse publicly. The recall affects the 2007-2010 model year Toyota Camry, 2004-2009 Toyota Prius, 2005-2010 Toyota Avalon, 2005-2010 Tacoma, 2007-2010 Toyota Tundra, 2007-2010 Lexus ES350 and 2006-2010 Lexus IS250 and IS350. NHTSA has investigated allegations of unwanted acceleration in Toyota vehicles eight times since 2003. Two probes, involving carpet panels in 2004 Toyota Sienna minivans, and floor mats in 2007 Lexus ES350 and 2007 Toyota Camry sedans, led to small recalls. The six other investigations were thrown out by the agency. In those investigations, however, NHTSA did find that the Toyota braking system could lose most of its power and effectiveness when the throttle is fully opened and that other aspects of vehicle design, including using push-button ignitions, could add risk in sudden-acceleration events. In the San Diego County case, NHTSA found that the floor mat in the sedan -- a loaner vehicle from an El Cajon car dealer -- was an all-weather mat intended for use in a Lexus sport utility vehicle. It also found that the design of the Lexus accelerator pedal may have enhanced the risk of it being obstructed by a floor mat. Toyota has continued to focus on the floor mats alone. On Monday in a video statement posted online, Toyota senior vice president Bob Daly addressed recent suggestions 'that there may be other causes of unintended acceleration' including problems with engine control systems, brake systems or electromagnetic interference. 'There is no evidence to support those theories,' Daly said. 'The question of unintended acceleration involving Toyota and Lexus vehicles has been repeatedly and thoroughly investigated by NHTSA, without any finding of defect other than the risk from an unsecured or incompatible driver's floor mat.' The response from federal regulators came as no surprise to Joan Claybrook, an auto safety activist who formerly headed NHTSA. 'The agency never says there is no defect. ... New information can come to light that there is a defect,' Claybrook said. 