Donald Trump's administration has told the UK to "reject two-tier policing" as the US sent its condolences to Henry Nowak's family.
The State Department, which is headed up by Marco Rubio, released a 41-word statement on Nowak's murder on social media.
In the statement, the State Department said: "Ideological conditioning and two-tiered policing are glaring symptoms of civilisational decline.
"They must be rejected across the West. The United States sends our condolences to the family of Henry Nowak and the people of the United Kingdom at this troubling time."
Mr Trump's relationship with Sir Keir Starmer has become increasingly fraught over the past six months, with the pair disagreeing over Greenland, Iran and the Chagos Islands.
The US President has also lashed out at the Prime Minister over free speech, North Sea oil and immigration.
The State Department's intervention also echoes Reform UK leader Nigel Farage's concerns following Nowak's murder.
Nowak, an 18-year-old finance student from Essex, was stabbed five times on the way home from a night out in December last year.
When officers arrived at the scene, Nowak told them he had been stabbed and that he could not breathe.
An officer was heard dismissing Nowak's cries for help, telling the teenager: "I don't think you have, mate."
Hampshire & the Isle of Wight Constabulary later revealed that officers had been misled by Sikh killer Vickrum Digwa.
Digwa, who was sentenced to life with a minimum tariff of 21 years, lied by claiming he had been the victim of a racist attack.
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