US President Barack Obama has hailed America's special relationship with Britain during a state banquet at Buckingham Palace.
Mr Obama told the British people they had been America's staunchest allies in the 10 years following the September 11 terrorist attacks on New York and Washington.
Some 170 guests at the banquet in London heard Mr Obama describe Britain as the United States' closest partner in the struggle to protect people from terrorist attacks and violent extremism around the world, despite very heavy sacrifices, the BBC reports.
The president paid tribute to Britain's military forces and said that both countries could have confidence in their partnership as they confronted the challenges of the 21st century together.
Mr Obama called the Queen a living witness to the power of the alliance and the chief source of its resilience.
The Queen, in turn, hailed the US as Britain's closest ally and gave a toast to what she called the "tried, tested and, yes, special relationship between our two nations".
She said: "I firmly believe that the strength of our links and many shared interests will continue to ensure that, when the US and the UK stand together, our people and other people of goodwill around the world will be more secure and can become more prosperous."
Mr Obama is on a three-day visit to Britain and is to meet with Prime Minister David Cameron for talks at Downing Street on Wednesday where the subjects of Afghanistan and Libya are expected to feature prominently, the BBC reports.
Mr Obama will also address MPs and peers in Westminster Hall.
The president and Mr Cameron are also due to drop in on a barbecue hosted by their wives for families of military personnel involved in joint UK-US missions overseas.
Earlier, Mr Obama and his wife Michelle met the newly married Duke and Duchess of Cambridge.
