The family of Harry Dunn, from left, mother Charlotte Charles, stepfather Bruce Charles, family spokesman Radd Seiger, father Tim Dunn and stepmother Tracey Dunn speak to the media outside the Ministry Of Justice in London, Friday, Dec. 20, 2019. (Photo: AP)

WASHINGTON, Dec. 20 (Xinhua) -- US State Department said Friday that British prosecutor's charge against Anne Sacoolas, an American diplomat's wife involving in a summer crash that killed a British teenager, was "not a helpful development."

Britain's Crown Prosecution Service (CPS) earlier in the day had authorized Northamptonshire Police to charge Anne Sacoolas with causing death by dangerous driving, according to an announcement by the CPS.

"May I remind all concerned that criminal proceedings against Anne Sacoolas are now active and that she has a right to a fair trial," Chief Crown Prosecutor Janine Smith said in the announcement.

The CPS also said it had started extradition proceedings through the Home Office.

British media reported that British Foreign Secretary Dominic Raab welcomed the decision to charge Sacoolas.

US Department of State responded later Friday that they were disappointed about the move by the British side.

"We are disappointed by today's announcement and fear that it will not bring a resolution closer," a State Department spokesperson said in a statement.

"We do not believe that the UK's charging decision is a helpful development," the statement added.

The statement also noted that the use of an extradition treaty to attempt to return the spouse of a former diplomat by force would establish "an extraordinarily troubling precedent."

Sacoolas' lawyer said her client "will not return voluntarily to the United Kingdom to face a potential jail sentence for what was a terrible but unintentional accident," according to media reports.

Harry Dunn, 19, of Charlton, Banbury, was killed when his motorbike crashed with a car near RAF Croughton on Aug. 27 in Northamptonshire in the East Midlands of England. The US State Department confirmed that the car driver was the spouse of a US diplomat assigned to Britain, who then left Britain using her diplomatic immunity.