The National Highway Traffic Safety Administration (NHTSA) is opening an investigation into 3 million vehicles from Kia and Hyundai due to thousands of reports of fires.

Reuters reports that the investigation comes in response to a petition from the Center of Auto Safety seeking a probe into the matter. The center has been investigating select Kia and Hyundai models for fire risks since 2007 and the most recent probe covers the 2011-2014 Kia Optima and Sorento, 2010-2015 Kia Soul, and the 2011-2014 Hyundai Sonata and Santa Fe.

It is claimed that there have been reports of more than 3,000 (!) fires, which injured over 100 people in Hyundai and Kia models.

The NHTSA initiated the probe after analyzing information from other manufacturers, consumer complaints, and other sources. Since 2015, more than 2.3 million Hyundai and Kia models have been recalled to address engine fire risks. This included more than 570,000 Sonata and Santa Fe models and 618,000 Optima, Sorento, and Sportage vehicles.

The agency says this new probe “is not limited to engine components and may cover additional vehicle systems or components.” In a statement, Hyundai said it was cooperating fully with the NHTSA.

The two South Korean carmakers have been the focus of attention for many investigators due to their handling of recalls for vehicles prone to fire risks. Late last year, it was revealed the federal prosecutors launched a criminal investigation into Hyundai and Kia to see if they had conducted these recalls properly. Additionally, Connecticut Attorney General William Tong recently said a number of U.S. states were investigating the companies for potential unfair and deceptive acts related to reports of fires in their vehicles.

Last month, Hyundai and Kia announced they will offer software upgrades for 3.7 million vehicles not being recalled.