The queen was accompanied by her husband Prince Philip and her grandson Prince William at the opening of the Flanders Fields Memorial Garden at the Wellington Barracks in central London.
A bugler at the event performed the Last Post, a British military trumpet call used to commemorate fallen soldiers.
The soil for the garden was gathered by schoolchildren from Britain and Belgium in 70 spots associated with World War I and it has taken a year to construct.
The area was designed by Belgian architect Piet Blanckaert and includes a bench made from Flemish bluestone and trees indigenous to the battlefields.
William's younger brother Prince Harry also laid a cross of remembrance at Westminster Abbey in front of two wooden crosses from the graves of unknown British soldiers from the First and Second World Wars.
The events came ahead of Remembrance Sunday on November 9, which marks the anniversary of the end of World War I.
There have been commemorations around the world this year on the 100th anniversary of the beginning of the war.
