Harry Dunn in an undated photograph. Image Credit: Supplied

An American woman, the wife of a US diplomat, has fled the United Kingdom after the death of a British teenager in a wrong-way collision, authorities said Saturday. Harry Dunn, 19, died after the wreck in which the 42-year-old woman allegedly collided with Dunn's motorcycle near the Royal Air Force Croughton station, which is operated by the US Air Force.

The incident has caused widespread outrage after authorities said the diplomat's wife claimed diplomatic immunity under international law, allowing her to avoid prosecution.

In an emotional plea on Saturday, Dunn's parents begged President Donald Trump to intervene and to send the diplomat's wife back to the U.K. Authorities have declined to identify the woman.

"President Trump, please listen," Dunn's mother, Charlotte Charles, said in an interview with Sky News. "We're a family in ruin. We're broken. We can't grieve. Please, please, let her get back on a plane, come back to the UK... We could understand how she's feeling, but more importantly, she needs to face justice, see what she's done."

Under the 1961 Vienna Convention on Diplomatic Relations, family members of diplomats living in other countries are covered by immunity, allowing them to avoid arrest for crimes and escape civil liability in most circumstances. However, the diplomat's home country can waive immunity - and that's what British authorities and Dunn's loved ones are calling for in this case.

Nick Adderley, chief constable for the Northamptonshire Police, said Sunday that he and the police chief had asked the US Embassy "in the strongest terms" to waive the woman's immunity "in order to allow the justice process to take place."

In a Sunday statement to The Washington Post, British Foreign Secretary Dominic Raab said that he "called the U.S. Ambassador to express the UK's disappointment with their decision, and to urge the Embassy to reconsider it."

The State Department did not immediately respond to a request for comment late Sunday, but previously told multiple media outlets that immunity is "rarely waived." Officials offered their "deepest sympathies" to Dunn's family, confirming that the diplomat's family is back in the US.

"Any questions regarding a waiver of immunity with regard to our diplomats and their family members overseas in a case like this receive intense attention at senior levels and are considered carefully given the global impact such decisions carry," the State Department's statement said.

Following the revelation Saturday that the American suspect had left, Dunn's parents launched a #Justice4Harry campaign that has since drawn the attention of British lawmakers and thousands of supporters. Charles told Sky News there was "barely a day that went by where [Harry] didn't go out riding on his bike," racking up 50,000 miles of travel on his black Kawasaki.

Dunn's family said he was hit around 8:30 pm about 400 yards from the Air Force facility. Dunn died at a hospital, Northamptonshire Police said.

During the investigation, the American woman cooperated "fully" with police, and assured them "she had no plans to leave the country in the near future," Northamptonshire Police Superintendent Sarah Johnson said in a statement Saturday.

But then police learned the driver would be claiming diplomatic immunity, and so they made an immediate waiver request to the U.S. Embassy in London, a spokeswoman told The Post. That request was denied, she said.

"We're disgusted, appalled, how she could be having this cloak wrapped around her," Dunn's father, Tim Dunn, told Sky News. "I'm angry that someone could do this and then get on a plane and go.

"I can't believe she's living with herself," he added.

American diplomats have been involved in numerous overseas deaths in recent decades, but have largely avoided punishment under diplomatic immunity, even amid tense pressure from the countries where those incidents took place.