Queen Elizabeth II's heralded return to major public duties has been put on hold, as royal officials announced Friday she would not attend next week's Commonwealth Day service.

The 95-year-old monarch had been scheduled to attend the annual event at Westminster Abbey in central London on Monday afternoon, joined by some 1,500 guests.

Her expected attendance had been seen as a return to work after a period of fragile health, during which she had a mild bout of Covid.

But Buckingham Palace said "after discussing the arrangements with the Royal Household, the Queen has asked the Prince of Wales to represent Her Majesty" instead.

Prince Charles, 73, is the queen's eldest son and heir, who is expected to take over from her as head of the 54-nation Commonwealth when he becomes king.

The queen, who has rarely been seen in public since October last year when she had an unscheduled overnight stay in hospital, turns 96 next month.

She tested positive for coronavirus on February 20, and developed what the palace said were "mild" Covid symptoms, which forced her to cancel a series of virtual audiences.

But she was well enough last week to meet visiting Canadian Prime Minister Justin Trudeau in person at her Windsor Castle home west of London.

The palace gave no reason for her pull-out of Monday's event, adding: "The Queen will continue with other planned engagements, including in-person audiences, in the week ahead."

The queen last month became the first British monarch in history to reign for 70 years. Public events for her Platinum Jubilee are planned for early June.

She is the queen and head of state in Britain and 14 other Commonwealth nations or realms around the world, including Australia, New Zealand and Canada.

Her position as head of the Commonwealth grouping, which comprises about a quarter of the world's population, has made her an enduring global figure.

 Key event

Doctors advised Elizabeth to slow down after her hospital stay, and she began cancelling a series of high-profile events.

In November, she pulled out of hosting world leaders at a UN climate change summit in Glasgow, and cancelled an appearance at the Remembrance Day parade due to a bad back.

She has been seen using a walking stick for the first time, and heard complaining about mobility issues, even before her Covid diagnosis.

Asked about her health, Trudeau -- in London for talks on Russia's invasion of Ukraine -- gave no indication of concern, saying she was "very interested" in current events.

But her non-attendance at a key event in the royal calendar will inevitably cause concern, with a forthcoming memorial service for her late husband, Prince Philip, due to take place on March 29.

The Duke of Edinburgh, who was married to the queen for 73 years, died aged 99 last April, just weeks short of his 100th birthday.

Great efforts have been made to protect the queen from the coronavirus pandemic and she has spent much of the past two years at Windsor, with few in-person engagements.

Even Philip's funeral was held under strict coronavirus restrictions, with just 30 mourners.

Monday's event would have seen her alongside Charles, other senior royals, as well as leading British politicians, and senior foreign diplomats.

The last Commonwealth Day service at Westminster Abbey was held in March 2020, as coronavirus cases spiralled and just before Britain locked down for the first time.

It was also the last royal event attended by the queen's grandson, Prince Harry, and his wife, Meghan, before their shock departure from the United States.

Her Platinum Jubilee year has not got off to the best of starts.

Her second son Prince Andrew settled a US civil claim for sexual assault, and police have announced a probe into one of Charles' charities.