A group of U.S. states have launched an investigation into engine fires involving Hyundai Motor and Kia Motors vehicles.

Connecticut Attorney General William Tong said in a statement on Monday that the investigation is looking into "potential unfair and deceptive acts or practices" by the South Korean automakers. 

The attorney general said his office is one of the leaders of an ongoing multi-state investigation into deeply troubling reports of spontaneous fires in Hyundai and Kia vehicles. 

Tong added that his office is aware of multiple fires involving vehicles in Connecticut, including some which allegedly have already been repaired through the recall process, calling it a serious matter.

According to Reuters on Monday, the South Korean automakers have recalled more than two-point-three million vehicles since 2015 to address various engine fire risks. 

The news agency reported previously that U.S. federal prosecutors launched a criminal investigation into Hyundai and Kia in November to determine if vehicle recalls linked to engine defects had been conducted properly.