LONDON (AP) — The United States has refused an extradition request from Britain for an American woman involved in a road accident that killed a U.K. teen.

Anne Sacoolas has been charged by British prosecutors with causing death by dangerous driving over the crash that killed 19-year-old motorcyclist Harry Dunn.

Dunn died in August after his motorbike collided with a car driven by Sacoolas outside RAF Croughton, a British military base in central England used by U.S. forces. Sacoolas, whose husband was an intelligence officer at the base, returned to the U.S. soon afterwards.

The State Department says Sacoolas had diplomatic immunity when she was in Britain, and to send her to face criminal charges would set “an extraordinarily troubling precedent.”

The British government on Friday called the U.S. decision “a denial of justice.” The Home Office said it was “urgently considering our options.”