President Donald Trump says the US will not foot the bill for Prince Harry and Meghan's security amid reports that the pair have moved to the US from Canada.
Mr Trump tweeted he was "a great friend and admirer of the Queen and the United Kingdom", but added: "They must pay!"
The couple said they had no plans to ask for publicly funded security in the US.
They have reportedly relocated to Meghan's home state of California amid the intensifying coronavirus outbreak.
They will formally step down as senior royals on 31 March and will no longer carry out duties on behalf of the Queen, but these arrangements will be reviewed after one year.
In a statement released through a spokesperson on Sunday, the couple said: "The duke and duchess have no plans to ask the US government for security resources. Privately funded security arrangements have been made."
I am a great friend and admirer of the Queen & the United Kingdom. It was reported that Harry and Meghan, who left the Kingdom, would reside permanently in Canada. Now they have left Canada for the U.S. however, the U.S. will not pay for their security protection. They must pay!— Donald J. Trump (@realDonaldTrump) March 29, 2020
The couple and their son Archie have spent much of this year residing in Canada's west coast, following a six-week Christmas break on Vancouver Island.
Last month, the Canadian government announced that it would stop providing security assistance to the family "in keeping with their change in status".
Now Mr Trump appears to have followed suit.
The family moved again last week to the Los Angeles area where Meghan was raised and where her mother, Doria Ragland, now lives, US media reports say.
The president's announcement comes as the novel coronavirus continues its steady march across the US. There are currently 143,532 confirmed cases - more reported diagnoses than any other country - and there have been 2,572 deaths.
In California, coronavirus cases continue to surge, with 6,266 cases and 130 reported deaths. Last week Governor Gavin Newsom issued a shelter-in-place order - ordering Californians to remain at home except for providing or accessing essential services - among the toughest directives across the country.
Prince Harry's father, the Prince of Wales, tested positive for coronavirus earlier this week, Buckingham Palace said, but "remains in good health".