The British government on Friday condemned a decision by the United States not to extradite an American woman involved in a fatal road accident. 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 after.

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."

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British Foreign Secretary Dominic Raab called the U.S. decision "a denial of justice."

"I called the U.S. ambassador earlier to express the government's disappointment about this decision," Raab said, adding that U.K. officials are "urgently considering our options."

Under the Vienna Convention on Diplomatic Relations, families of diplomats are granted immunity from arrest or detention. British prosecutors, however, maintain that immunity does not apply to dependants of consular officials based outside London.

Dunn's family has urged Sacoolas to return and face British justice, and met with U.S. President Donald Trump in Washington as part of their campaign.

The AFP reports Dunn's parents were informed of the decision in a phone call with their MP on Thursday and "were not at all surprised", said family spokesman Radd Seiger.

"This is a lawless, corrupt administration that appears intent on attacking even its closest international ally," he said.

"If Trump and Pompeo think this is an end to the matter, they have another thing coming to them," he said, saying the family would meet the government to discuss their next steps.

Dunn's parents, Charlotte Charles and Tim Dunn, visited the White House in October to meet President Donald Trump. They said he was warm and welcoming but they criticized the White House's attempts to engineer a snap meeting with Sacoolas, who was in a room next door with photographers.

Meanwhile, Dunn's parents are filing the suit in Virginia, where Sacoolas lives, in hopes of compelling her to return to England, turn herself in and face charges.

"She needs to still face what she's done to us and take some punishment for that," Charles Dunn told CBS last month.