United States authorities are reportedly looking into airbag failures in recent deadly crashes of Hyundai and Kia vehicles.

According to Reuters, the U.S. National Highway Traffic Safety Administration announced on Saturday that it is opening a probe into why some air bags failed to deploy in Hyundai and Kia vehicles after crashes in which four people were reportedly killed and another six injured.

The administration reportedly said it was reviewing 425-thousand 2012-2013 Kia Forte and 2011 Hyundai Sonata cars.

The administration said it was aware of six crashes in which six people were injured when air bags failed to deploy in frontal crashes, including four in 2011 Hyundai Sonatas and two in 2012 and 2013 Kia Fortes.