The Queen pulled out of Monday's Commonwealth Day service at Westminster Abbey, which was to have been her first public engagement since leaving hospital last week after a bout of gastroenteritis.
The Queen, 86, did attend an evening reception at Marlborough House for Commonwealth heads of state to sign a charter backing equal rights in all 54 Commonwealth nations.
A spokeswoman at Buckingham Palace said it was decided the Queen should continue to rest during the day to recover from her illness, and it was too early to say how engagements for the rest of the week would be affected.
The charter, agreed by the Commonwealth nations in December, expresses "implacable" opposition "to all forms of discrimination, whether rooted in gender, race, colour, creed, political belief or other grounds". The Queen's recorded Commonwealth Day message praised the shared values of "peace, democracy, development, justice and human rights".
The Queen's health is generally thought to be remarkable. She spent just one night at the King Edward VII hospital on Sunday 3 March, her first hospital stay in a decade, after two days' illness. She left hospital waving cheerfully to the assembled staff, and was said by Buckingham Palace to be in "good spirits" as she returned to convalesce at Windsor Castle.
She pulled out ofplanned visits to Wales for St David's Day celebrations and Italy, where she had been due to meet President Giorgio Napolitano..
The Queen's remaining engagements this week include visits to hi-tech companies in the East End of London and a service at the Guard's Chapel at the Wellington Barracks in London to mark the 175th anniversary of the Soldiers' and Airmen's Scripture Readers Association.
The Duke of Edinburgh has been taking the place of the Queen at several engagements, although he was warned to cut down his workload, at the age of 91, after several hospital admissions last year.
The private King Edward VII, the hospital of choice for the royals, made world headlines in December when staff fell for a hoax call from an Australian radio station, and gave information on the condition of the Duchess of Cambridge, who was being treated for acute morning sickness in early pregnancy. The nurse who initially took the call later killed herself.
