(CNN) The United States has declined the United Kingdom's request to extradite American citizen Anne Sacoolas, the wife of an American diplomat, who was charged with causing the death by dangerous driving of British teenager Harry Dunn last August.

A State Department spokesperson cited Sacoolas' diplomatic status at the time of the accident and said granting such an extradition "would render the invocation of diplomatic immunity a practical nullity and would set an extraordinarily troubling precedent.

"The United States has a history of close law enforcement cooperation with the United Kingdom, and we value that relationship," the spokesperson said. "The United States government again expresses its sincere condolences and sympathy to the Dunn family for the loss of their son."

The US' decision to decline extradition comes after the UK's Crown Prosecution Service said last month that it had started extradition proceedings after Sacoolas was charged in the case of Dunn.

Harry Dunn was riding a motorcycle when he was struck by a vehicle that was traveling on the wrong side of the road.

Dunn, 19, was killed August 27 in Croughton in central England, which is home to a Royal Air Force station controlled by the US Air Force. UK police say Dunn was riding a motorcycle when he was struck by a vehicle that was traveling on the wrong side of the road.

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