Britain on Friday rebuked the United States for refusing to extradite a diplomat's wife charged over a car crash that killed a British teenager, calling it a "denial of justice".
The case of Anne Sacoolas has been a thorn in London's close relations with Washington, stirring up debates over the limits of diplomatic immunity in cases unrelated to national security.
Foreign Secretary Dominic Raab said he expressed disappointment at the decision in a call to Woody Johnson, the U.S. ambassador to Britain.
"We feel this amounts to a denial of justice, and we believe Anne Sacoolas should return to the U.K. We are now urgently considering our options," said Raab. "The U.K. would have acted differently if this had been a U.K. diplomat serving in the U.S."
Harry Dunn, 19, died in August when his motorcycle collided with a car driving on the wrong side of the road near an Air Force base in Croughton, central England, used by the U.S. military as a communications hub.
Sacoolas, who has admitted to being the driver, was charged by British police with causing death by dangerous driving.
However, she has cited immunity while refusing to return to Britain to face justice, as Dunn's parents have demanded.
U.S. Secretary of State Mike Pompeo has decided to reject Britain's extradition request.
'Lawless, Corrupt Administration'
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 U.S. 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.
The U.S. State Department confirmed it had rejected the extradition request, saying Sacoolas had immunity from criminal jurisdiction during her stay in the U.K.
"If the United States were to grant the U.K.'s extradition request, it would render the invocation of diplomatic immunity a practical nullity and would set an extraordinarily troubling precedent," it said in a statement.
The case has been a political headache for Prime Minister Boris Johnson, who is cultivating trade relations with Washington in a bid to offset the potential damage of Britain's withdrawal from the EU.
Trump has called the crash a "terrible accident," saying it is common for Americans in Britain to have difficulty driving on the left side of the road.