LONDON, April 21 (Xinhua) -- The 91st birthday of Britain's monarch Queen Elizabeth II was marked with a series of gun salutes across the country on Friday.

First World War artillery pieces manned by the King's Troop, Royal Horse Artillery, fired a 41-gun salute in London's Hyde Park at midday, which lies next door to the Queen's official residence at Buckingham Palace.

The 41 rounds fired in the Park are the standard 21-gun salute plus 20 rounds because it is a royal park.

A 62-gun salute was fired at the Tower of London at 1 p.m. by the Honourable Artillery Company, using modern artillery pieces.

The 62 rounds fired at the Tower are made up of 21 for a royal salute, plus a further 20 because the Tower is a royal palace and fortress, plus another 21 because it is located in the City of London.

A further two 21-gun salutes were also fired at Edinburgh Castle and Stirling Castle in Scotland.

The press office for the Queen also announced Friday that the upcoming state visit to the country by the Spanish King Felipe VI, scheduled for June 6-8, had been postponed by the two monarchs as Britain will be holding a general election on June 8.

The state visit will now take place from July 12 to 14.