US regulators are investigating General Motors’ Cruise autonomous vehicle division after reports of incidents where self-driving cars may not have used proper caution around pedestrians.

The National Highway Traffic Safety Administration (NHTSA) said the reports involve automated driving system (ADS) equipped vehicles encroaching on pedestrians on or entering roads, including crossings.

This could raise the risk of a vehicle striking a pedestrian, which could result in severe injury or death, according to the NHTSA.

The NHTSA’s Office of Defects Investigation (ODI) said that it has received two reports involving pedestrian injuries from Cruise vehicles.

It has also identified two additional incidents from videos posted to public websites. The office said the total number of relevant pedestrian incidents is unknown.

“Cruise’s safety record over 5 million miles continues to outperform comparable human drivers at a time when pedestrian injuries and deaths are at an all-time high,” Cruise spokesperson Hannah Lindow said in a statement.

“Cruise communicates regularly with NHTSA and has consistently cooperated with each of NHTSA’s requests for information – whether associated with an investigation or not – and we plan to continue doing so.”

The ODI said its investigation is being opened to help determine the scope and severity of the potential problem, including causal factors that may relate to ADS driving policies and performance around pedestrians, and to fully assess the potential safety risks.

In August, General Motors’ Cruise unit agreed to cut its fleet of San Francisco robo-taxis in half as authorities investigated two crashes in the city.

The state Department of Motor Vehicles asked for the reduction at the time after a Cruise vehicle without a human driver collided with an unspecified emergency vehicle.