The British Monarchy posted on its official Twitter feed:
US President Barack Obama has praised those competing in the Invictus Games in a special video message.
The President said he knew it would be "fiercely competitive few days" as teams from around the world prepared for the Paralympics-style championships.
"The truth is that everyone of you in these Games, every service member and veteran, has already earned our highest admiration and our deepest gratitude," Obama said.
"When your countries asked you to serve, to risk everything to protect our safety and our freedom, you and your families answered the call and just as you inspire us with your courage on the battlefield, your grit and resilience when you take the playing field, your incomparable souls inspire us today."
Prince Harry says the Invictus Games are about supporting the individuals taking part and not the war.
Some 400 wounded service personnel from 13 countries are taking part in the Games, an international sporting event for wounded, injured and sick Servicemen and women.
Harry has championed the Games with the Duke and Duchess of Cambridge also supporting them.
Prince Harry has said he feels 'young at heart' ahead of turning 30 on September 15.
Speaking after presenting medals at the Invictus Games, he said: 'I'm slowly starting to feel old. I think 30 is one of those first milestones when you drive through a village and see the 30mph sign. It's that constant reminder going 'I am actually quite old'.
'But I don't feel too old. I think i'm always young at heart', the Prince added.
A new wax model of Prince Harry has gone on display at Madame Tussauds in London to celebrate his 30th birthday.
The new figure shows the Prince in combat uniform to reflect his job as a captain in the Army Air Corps.
The figure cost £150,000 and took a team of sculptors and artists four months to create.
The countdown to the Invictus Games begins later today when Prince Harry welcomes team captains from across the globe to London.
The competition for wounded servicemen and women, both serving and veterans, has attracted 12 foreign teams and a UK contingent who will compete in the four-day event, which begins on Thursday.
The Games will also be supported by Harry's immediate family with the Prince of Wales, Duchess of Cornwall and the Duke and Duchess of Cambridge attending heats and matches in the run up to the main event.
More than 400 competitors will go head-to-head in nine adaptive sports at the Queen Elizabeth Olympic Park and Lee Valley Athletics Centre in London.
Prince Harry's speech to introduce Team GB's athletes for the Invictus Games did not quite go according to plan.
Firstly, his notes blew away and then a vocal canine decided he wanted some of the limelight too.
The Invictus Games is an international Paralympic-style event for wounded soldiers.
The Games are being held in London 10-14 September.
"To see young lads — much younger than me — wrapped in plastic and missing limbs.......was something I never prepared myself for."Read the full story ›
The medals and medallions, which will be given to each of the 400 participants of the Paralympic-style Invictus Games, have been unveiled.Read the full story ›
The Duke and Duchess of Cambridge were joined by Prince Harry as they met the families of soldiers who fought in the First World War.