LONDON — Prime Minister Boris Johnson called on Monday for the wife of an American diplomat involved in a crash that killed a teenager to return to Britain, saying he would ask President Trump to intervene if the impasse was not resolved through diplomatic channels.
Mr. Johnson’s statement — in which he also disclosed the woman’s identity — aggravated tensions in a trans-Atlantic relationship that started fraying after Mr. Trump feuded publicly with other British officials and denounced Britain’s ambassador to Washington, forcing him to give up his post.
“I do not think that it can be right to use the process of diplomatic immunity for this type of purpose,” Mr. Johnson said in an interview with the BBC on Monday, “and I hope that Anne Sacoolas will come back and will engage properly with the processes of laws that carried out in this country.”
Mr. Johnson added that, if necessary, he would raise the issue “personally with the White House.”
The British authorities have been pressing the United States to reconsider its refusal to intervene in an investigation of the crash on Aug. 27, after Ms. Sacoolas, an American citizen who has diplomatic immunity, left Britain despite telling the police that she had no plans to do so.
Harry Dunn, 19, was killed after his motorcycle collided with a car traveling in the opposite direction in Brackley, a town about 60 miles northeast of London that is near R.A.F. Croughton, a Royal Air Force base that is the site of a United States Air Force communication station.
The police have said that Ms. Sacoolas, who is 42, was driving on the wrong side of the road when the crash occurred, and that their investigation has been complicated by the fact that she left the country.
The developments have prompted a diplomatic tug-of-war, after Britain transmitted a formal request for a waiver of immunity to the United States Embassy in London on Sept. 5 that was declined eight days later.
The embassy on Monday declined to confirm the woman’s identity — she is reportedly the wife of an American diplomat — but said, it was unlikely to lift immunity in the case.
Superintendent Sarah Johnson, head of operations for the Northamptonshire police, said in a statement on Saturday that the police had sought documentation “to allow for the arrest and formal interview of the subject.”
“Harry Dunn’s family deserves justice, and in order to achieve this, a full and thorough investigation, with the assistance of all parties involved, needs to take place,” she said.
The police are also working closely with the Foreign and Commonwealth Office, Ms. Johnson said, adding that they were “exploring all opportunities through diplomatic channels” to ensure the investigation’s progress.
Harry Dunn’s mother, Charlotte Charles, has been pushing to have the American woman’s immunity waived and for her to return to Britain.
“President Trump, please listen,” Ms. Charles told Sky News, the outlet that first reported on the identity of the 42-year-old woman. “We’re a family in ruin. We’re broken.”
“We can’t grieve,” she said, adding of the woman, “Please, please let her get back on a plane.”
Dominic Raab, the foreign secretary, offered his condolences to the victim’s family and released a statement addressing the matter.
“I have called the U.S. ambassador to express the U.K.’s disappointment with their decision, and to urge the embassy to reconsider it,” Mr. Raab said.
The United States Embassy said that questions about immunity, which is rarely waived, were discussed at senior levels and that it was in close contact with the British authorities.
After news of the woman’s flight from Britain emerged, the news media, the British government and social media users stepped up pressure on the American government to reconsider her immunity and allow the police to resume questioning her in Britain.
“We have to get proper justice for Harry and closure for his family,” Andrea Leadsom, the secretary of state for business, energy and industrial strategy, wrote on Twitter on Saturday. She wrote that she had met Harry Dunn’s family a day earlier, and that they were “heartbroken.”
“Harry & his family have been wronged,” Angela Rayner, a member of Parliament for the opposition Labour Party, said in a tweet.
The crash, the investigation, and Mr. Johnson’s identification of the American woman could further strain the so-called special relationship between the two countries, which has already been tested numerous times during Mr. Trump’s presidency.
Still, Britain must walk a fine line, most notably because it is hoping to sign a trade deal with the United States after it leaves the European Union, a fraught process that is complicated by the fact that the Americans may make demands the British find unacceptable.
Robert Singh, a professor of politics at Birkbeck, University of London, who specializes in American foreign policy, said that he cannot recall a more serious immunity dispute between the two countries.
He said in an email that while the police could visit the suspect in the United States, such a visit would most likely be of limited value. “This merely seems to postpone the moment of reckoning,” he said. “If she is indeed guilty of the crime, as alleged, then there will be immense pressure upon the U.K. government to initiate formal extradition proceedings — which, one would imagine, any U.S. administration (and this one, in particular) will resist.”
The victim’s parents said they would continue fighting to get justice for their son’s death.
“We are not going to be swept under the carpet,” Ms. Charles told ITV, a British news channel. “If that becomes his legacy, then we are going to carry on fighting, we’re not going to give up, we’re not going to go away,” she said.
“We can’t let our son die and nothing be answered for,” said Tim Dunn, his father.