LONDON (Reuters) - Britain's 86-year-old Queen Elizabeth has canceled a planned trip to the Welsh city of Swansea because of a stomach upset, Buckingham Palace said on Friday.

"She will be assessed in the coming days but her majesty is currently spending the weekend at Windsor as usual," said a palace spokesman, referring to her official residence.

The spokesman added the monarch, who had been due to attend a military ceremony in the south Wales city on Saturday, was experiencing symptoms of gastroenteritis, an infection of the stomach and bowel caused by bacteria or viruses.

Queen Elizabeth marked 60 years on the throne last year and remains hugely popular in Britain.

(Reporting by Maria Golovnina; Editing by Jason Webb)