The US state department has labelled an extradition request for the American woman charged with causing the death of a teenage motorcyclist in Northamptonshire as “highly inappropriate”.

The Home Office sent an official demand on Friday that Anne Sacoolas be returned to the UK.

The 42-year-old – the wife of an American intelligence officer – is wanted to stand trial for causing the death of 19-year-old Harry Dunn by dangerous driving following a collision last August.

The youngster, from the village of Charlton, died after his motorbike crashed into a car outside the nearby RAF Croughton base.

It is believed the car was being driven by Ms Sacoolas and was on the wrong side of the road at the time.

But, after police attended the scene, she later fled to the US claiming diplomatic immunity and sparking a transatlantic controversy.

Now, after the Home Office made its extradition request, officials there said the matter was “a decision for the US authorities”.

But the US Department of State appeared in little mood for considering the approach late on Friday night.

A spokesperson said: “The use of an extradition treaty to attempt to return the spouse of a former diplomat by force would establish an extraordinarily troubling precedent.”

They added the department would continue to engage with the UK government and said it had been transparent on all legal and diplomatic matters raised by the case.

Confirming the initial request, a spokesperson for the Home Office said: “Following the Crown Prosecution Service’s charging decision, the Home Office has sent an extradition request to the United States for Anne Sacoolas on charges of causing death by dangerous driving.

“This is now a decision for the US authorities.”

Speaking before the US response, Radd Seiger, the Dunn family’s spokesperson, said: “This will not of course bring Harry back, but in the circumstances of all that this family have been through, they are pleased with the development and feel that it is a huge step towards achieving justice for Harry and making good on the promise that they made to him on the night he died that they would secure justice for him.”

He added: “No one, whether diplomat or otherwise, is above the law.”

Under the treaty that exists between the UK and US, the British government is responsible for considering and forwarding extradition requests to the US state department once they have been certified by a judge.

State department officials are then responsible for considering the approach before handing it over to the Department of Justice and the US courts.