The Duke of York has provided "zero co-operation" to an inquiry into late sex offender Jeffrey Epstein, the prosecutor in charge of the investigation has said.
Prosecutors and the FBI have contacted his lawyers but have received no reply, said US attorney Geoffrey Berman.
Prince Andrew says he did not see, or suspect, any suspicious behaviour when visiting homes of his then friend.
Buckingham Palace said the prince's legal team was dealing with the issue.
It said it would not be commenting further.
Convicted US sex offender Epstein took his own life in a jail cell in August, aged 66, while awaiting trial on sex trafficking and conspiracy charges.
Mr Berman, the US Attorney for the Southern District of New York, said the FBI and Southern District of New York had requested to interview the duke as part of their inquiry into Epstein's crimes, but "to date, Prince Andrew has provided zero co-operation".
Prince Andrew has come under fire for his friendship with the US financier, who was jailed in Florida in 2008 for procuring a minor for prostitution.
He told BBC Newsnight in November that he first met Epstein in 1999 and did not regret their friendship - which led to Epstein attending events at Windsor Castle and Sandringham - because it had "some seriously beneficial outcomes".
However he admitted it was wrong of him to visit Epstein at his home in 2010, after his conviction.
Virginia Giuffre, one of Epstein's accusers, says she was trafficked to London by Epstein in 2001, when she was 17, and forced to have sex with Prince Andrew.
Prince Andrew emphatically denies any form of sexual contact or relationship with her and says any claim to the contrary is false and without foundation.
He said he has no recollection of ever meeting the woman, who was previously known as Virginia Roberts.
'Willing to help'
Prince Andrew was accused of lacking empathy for Epstein's victims in his Newsnight interview and failing to show regret over their friendship.
Shortly after it was broadcast, the prince announced he was stepping back from royal duties for the "foreseeable future" because the Epstein scandal had become a "major disruption" to the Royal Family.
At the time, he said he was "willing to help any appropriate law enforcement agency".
He also said in the BBC interview he would consider giving evidence under oath "if push came to shove and the legal advice was to do so".
The lawyer for Epstein's victims has since said he plans to serve subpoenas for the prince to be questioned under oath.
Prince Andrew accompanied the Queen to church near Sandringham earlier this month.
It was the Queen's first public appearance after the Duke and Duchess of Sussex were revealed to have given up their HRH titles - and the first time the prince had been seen with his mother since the week after his Newsnight interview.
Prosecutor Mr Berman made his comments at a news conference outside Epstein's New York mansion.
He was speaking at an event to promote a new law that makes it easier for victims to sue over childhood abuse.
Before being asked about Prince Andrew, he spoke about the progress of the sex trafficking investigation and said it was looking at possible "conspirators" who had worked alongside Epstein procuring girls for the financier's sexual gratification.
"Jeffrey Epstein couldn't have done what he did without the assistance of others, and I can assure you that the investigation is moving forward," he said.