BERLIN (AP) — An assailant stabbed the driver of a car in western Germany early Sunday and investigators weren't ruling out an Islamic extremist motive for the attack, police said.

Shortly after midnight, the unidentified assailant opened the door of a car that was driving slowly through Stolberg, near Aachen and close to the Belgian border, police said on Twitter. He stabbed the driver, who sustained wounds to the arm and later underwent an operation. Police said the injuries weren't life-threatening.

They said the assailant is being sought nationwide and that police in the regional hub of Cologne took over the case “because an Islamist background cannot be ruled out.”

They wouldn't confirm or deny reports in the Bild and Aachener Zeitung newspapers that the assailant shouted “Allahu akbar," or “God is great” in Arabic.