A senior Washington official on Wednesday refused to comment on a mass leak of classified US documents that suggest British special military forces have been operating inside Ukraine.
The UK had as many as 50 highly trained military personnel in Ukraine between February and March, according to files which appeared online.
Other Nato members also allegedly have more than a dozen special forces members in the country, including Latvia (17), France (15) and the US (14), the document dated March 23 suggested.
The leak was revealed as President Joe Biden began a four-day visit to Northern Ireland to mark the 25th anniversary of the Good Friday Agreement.
Amanda Sloat, a special assistant to the President and the National Security Council’s Senior Director for Europe, refused to comment on how it was impacting conversations with her European counterparts.
In a press conference on Wednesday she said she would like to “focus here for now on [Mr Biden’s] trip” to Belfast.
UK special forces, regarded to be among the most capable in the world, are made up of elite military units with distinct areas of expertise.
The files appear to confirm speculation that has circulated since Russia launched its full scale invasion last February.
It is likely to be seized upon by Moscow leaders, who have argued in recent months that they are not just challenging Ukraine but Nato as well.
The disclosure of the papers has also rocked Washington, exposing extensive details of US intelligence gathering.
Some files marked “top secret” reveal sensitive information about the war and Kyiv’s preparations for a spring counter-offensive.
Others show that Egypt allegedly had plans to produce 40,000 rockets for Russia in secret and that South Korea was torn about selling weapons for use in Ukraine.
The disclosures prompted questions about how the US was able to intercept such a high-level conversations between foreign leaders and diplomats.
The British Ministry of Defence refused to comment on the leak on Wednesday.
But it previously warned against taking the allegations in the papers at “face value”.
“The widely reported leak of alleged classified US information has demonstrated a serious level of inaccuracy,” the MoD said.
“Readers should be cautious about taking at face value allegations that have the potential to spread disinformation.”
The British Government did not elaborate on which documents it was referring to.
One file detailing the number of casualties suffered by both Russia and Ukraine published on messaging app Discord appeared to have been doctored.
Pentagon officials have said the documents are real and US Defense Secretary Lloyd Austin confirmed that the Department of Justice had opened a criminal investigation to find the source of the leak.
“We will continue to investigate and turn over every rock until we find the source of this and the extent of it,” he said.
