Meghan Markle has accused the British royal family of peddling lies against herself and her husband Prince Harry, in an escalating transatlantic war of words before a tell-all interview with US chat show host Oprah Winfrey.

The explosive claim is the latest salvo in an increasingly heated public relations battle between the British institution and the US-based couple.

Harry and Meghan, who married in a fairytale wedding in 2018, stepped down from frontline royal duties last year, in part blaming media intrusion for their decision to move to North America.

But a steady drip of stories in Britain about the Duke and Duchess of Sussex, as they are formally known - and tit-for-tat responses - is becoming a torrent as the broadcast approaches this weekend.

The new clip released by US broadcaster CBS came just hours after Buckingham Palace said it was probing claims that Meghan had bullied royal household staff during her time in Britain.

"I don't know how they could expect that after all of this time we would still just be silent if there's an active role that 'The Firm' (the royal family) is playing in perpetuating falsehoods about us," she told Winfrey in the clip from the upcoming interview.

Battle for public sympathy

There was no immediate response from Buckingham Palace but comments sparked a predictable frenzy in the British media.

Veteran royal commentator Richard Kay likened the row to the "War of the Waleses" in the 1990s when the marriage of Harry's parents crumbled.

Heir-to-the-throne Charles, the Prince of Wales, and Diana, princess of Wales, gave unprecedented television interviews that lifted the lid on their troubled relationship -- and extra-marital affairs.

That was a similar "bitter and acrimonious battle for public sympathy" to Harry and Meghan, he wrote in the Daily Mail.

But Omid Scobie, royal editor of Harper's Bazaar US, and co-author of a sympathetic biography of Harry and Meghan, "Finding Freedom", said it was merely a chance for them to tell their side of the story.

He told AFP that Meghan, a mixed-race former television actress, was likely to address the racism she faced in the British press and on social media, as well as their "troubles" in the monarchy itself.

But he added: "I think, as is often the case, the noise usually happens before the event itself when it comes to the royal family and the coverage surrounding it.

"In the end it ends up being OK and I think that that'll be exactly the same with this Oprah special. Ultimately Harry and Meghan want to start their next chapter on a positive note."

Royal biographer Penny Junor, however, said the couple's interview, scheduled to be broadcast in the United States on Sunday, and in Britain early Monday, was "obviously very bad timing".

Harry's grandfather, Queen Elizabeth II's husband Prince Philip, 99, has been in hospital for more than two weeks, and on Wednesday underwent a procedure on a pre-existing heart condition.

"I would have thought he'd be aware of it and it's not helpful," Junor said, accusing the couple of spending the last year "courting publicity".

"I don't think doing this interview was a good idea in the first place."

'History repeating itself'

Harry and Meghan's acrimonious split from the royal family was made permanent last month, when the queen removed their honorary titles and patronages.

That followed nearly 12 months in which both sides have tried to control the narrative of their departure, which has polarised opinion on both sides of the Atlantic.

Harry, 36, said in a clip of the Winfrey interview released earlier this week that he feared "history repeating itself" had they stayed, in a reference to the press hounding of his mother.

Diana died in a high-speed car crash after being relentlessly pursued by photographers through Paris in August 1997.

The bullying allegations, first reported in The Times newspaper on Wednesday, however, step up the war of words, with some commentators likening it to the constitutional crisis of 1936.

Then, king Edward VIII abdicated to marry Wallis Simpson, who like Meghan was an American divorcee.

Meghan, who is 39 and pregnant with the couple's second child, said the latest claims against her were a character assassination, and an attempt to "peddle a wholly false narrative" before the Winfrey interview is broadcast.

Since relocating to the US, Harry and Meghan have launched legal action against a number of media publications, alleging invasion of privacy.