The US State Department has said the decision to refuse an extradition request for Harry Dunn's alleged killer is final, amid claims of an Interpol Red Notice being issued for her arrest.
The teenage motorcyclist's family were told by Northamptonshire Police onMonday that 42-year-old Anne Sacoolas was "wanted internationally" inconnection with his death.
In an email to the 19-year-old's parents, seen by the PA news agency, the force said "the wanted circulations should be enacted" if Sacoolas left the US.
But a spokeswoman for the US State Department maintained the position that the suspect had diplomatic immunity from criminal jurisdiction.
She said that granting the extradition request for Sacoolas would have rendered the invocation of diplomatic immunity a practical nullity and would have set an extraordinarily troubling precedent.
The spokeswoman added that US Secretary of State Mike Pompeo's decision to decline the UK's request for extradition was final.
Mr Dunn was killed when his motorbike crashed into a car outside a US military base in Northamptonshire in August last year.
Sacoolas, the wife of a US intelligence official based at RAF Croughton,claimed diplomatic immunity following the crash and was able to return to her home country, sparking an international outcry.
She was charged with causing death by dangerous driving in December but the extradition request from the Home Office was rejected the following month.
On Monday, Dunn family spokesman Radd Seiger tweeted to say: "For those slightly confused, I can confirm that Interpol have circulated a Red Notice in respect of Anne Sacoolas."
Shadow foreign secretary Lisa Nandy said the decision to issue a Red Notice highlighted the "clear and repeated failings of the Foreign Office" in dealing with the case.
The Red Notice is not an international arrest warrant, but is issued forfugitives wanted for prosecution or sentencing.
The process is normally used so member countries can look out for the suspect, which usually assists with extradition proceedings.
We are utterly bereft and heartbroken and miss our Harry every minute of every single day. This is important news that Radd has just passed on to us and we are in pieces. I just want to urge Mrs Sacoolas to come back to the UK and do the right thing.
The spokeswoman for the State Department said the US has a history of close law enforcement co-operation with the UK, and values that relationship.
She added that since the tragic accident occurred, the US has been closelyengaged with the UK Government, and has been transparent about positions on legal and diplomatic matters concerning the accident.
Mr Seiger said pressure was growing on the White House to send Anne Sacoolas back to face justice.
"No-one will ever accept the State Department's position that it is acceptable for anyone to kill a young person and just walk away. They are in fantasy land if that is what they really believe.