The federal government has upgraded an investigation into the 2007 Lexus ES350 sedan after at least 12 people were injured when the vehicle accelerated without warning.

According to the Associated Press (AP), the National Highway Traffic Safety Administration (NHTSA) said in a report 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 reportedly said.

The report said Toyota told NHTSA it sent a mailing to ES350 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.

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

Lexus spokesman Greg Thome told the news agency that, because the investigation is ongoing, it's too early to say whether floor mats are definitely causing the alleged defect.

NHTSA told AP it and Toyota had received 40 complaints about unintended acceleration. Eight crashes have been reported, including one that caused a seven-vehicle pileup.

In some cases, drivers travelled several miles at speeds of more than 90 mph before they were able to stop, NHTSA was reported to have said.