Queen Elizabeth will miss a planned virtual engagement on Tuesday because she is still experiencing mild cold-like symptoms after testing positive for COVID-19, a spokesman for Buckingham Palace said.

The palace announced that the queen had tested positive on Sunday but was expected to carry on with light engagements, an indication that the world's current oldest and longest-reigning monarch was not seriously unwell.

She sent a message of condolence to Brazil on Monday to say she was deeply saddened by recent fatal floods, and was planning to go ahead with other virtual diplomatic audiences scheduled with foreign ambassadors, the palace said.

She will now decide nearer to the time whether to press ahead with further engagements this week, such as her weekly conversation with Prime Minister Boris Johnson on Wednesday.

News of the positive test has sharpened concerns about the health of the world's longest-reigning monarch two weeks after she marked 70 years on the British throne.

The 95-year-old queen, who has been fully vaccinated against coronavirus, quipped last week to Palace staff that she could not move much, and she spent a night in hospital last October for an unspecified ailment.

(Reporting by Michael Holden; writing by Kate Holton, Editing by Kylie MacLellan and Elizabeth Piper) ((kate.holton@thomsonreuters.com; 0044 207 542 8560; Reuters Messaging: kate.holton.thomsonreuters.com@reuters.net))