Fears grew on Thursday for Queen Elizabeth II after Buckingham Palace said her doctors were "concerned" for her health and recommended that she remain under medical supervision.
The 96-year-old head of state -- Britain's longest-serving monarch -- has been dogged by health problems since last October that have left her struggling to walk and stand.
The queen -- an instantly recognisable figure to billions of people across the world -- is in her Platinum Jubilee year, marking 70 years since she succeeded her father king George VI in 1952.
All her children -- heir to the throne Prince Charles, 73, Princess Anne, 72, Prince Andrew, 62, and Prince Edward, 58, were either at or heading to Balmoral, royal officials said.
On Wednesday, the queen pulled out of a planned meeting with her senior political advisors, after being told to rest.
The previous day she held audiences at her Scottish Highlands retreat, Balmoral, with outgoing prime minister Boris Johnson and appointed his successor, Liz Truss.
"Following further evaluation this morning, the queen's doctors are concerned for Her Majesty's health and have recommended she remain under medical supervision," Buckingham Palace said in a statement.
"The queen remains comfortable and at Balmoral," the palace added.
The palace statement about the queen's health is highly unusual.
"The palace does not issue bulletins on the queen's health unless it's significant," royal commentator and author Robert Hardman told the BBC.-AFP
