DETROIT (AP) _ The U.S. government has upgraded an investigation into the 2007 Lexus ES 350 sedan after at least 12 people were injured when the vehicle accelerated without warning.

The National Highway Traffic Safety Administration said in a report issued this week that an all-weather floor mat can trap the throttle pedal when it's not properly secured, resulting in unwanted acceleration. The all-weather floor mat has been found in a majority of the vehicles that reported the problem, NHTSA said.

Toyota Motor Corp. told NHTSA it sent a mailing to ES 350 owners in late April warning them about improper installation of the all-weather floor mat. The mat should be secured with clips and shouldn't be placed over the standard floor mat. Toyota also said it changed the labelling on the floor mat.

NHTSA is now deciding whether Toyota's actions were sufficient. Vehicle investigations can lead to product recalls. There are 98,454 ES 350 sedans on the road.

Lexus spokesman Greg Thome said because the investigation is ongoing, it's too early to say whether floor mats are definitely causing the alleged defect. Thome said owners should call the company's customer service number if they have questions.

NHTSA and Toyota have received 40 complaints about unintended acceleration, NHTSA said. Eight crashes have been reported, including one that caused a seven-vehicle pileup. In some cases, drivers travelled several kilometres at speeds of more than 145 km/h before they were able to stop, NHTSA said.

Note: The Lexus Customer Service Line can be reached at 1-800-255-3987