|Obama conducted a ceremonial review of a Scots Guard regiment as part of his stay [Reuters]
Barack Obama, the US president, has called the partnership between his country and the UK "an essential relationship for us and the world" as he arrived in London for a three-day trip.
In a joint article written by the US leader and David Cameron, the British prime minister, in The Times newspaper, the pair put their ties at the heart of the drive for global stability and prosperity.
"When the United States and Britain stand together, our people and people around the world can become more secure and more prosperous," they wrote.
"Ours is not just a special relationship, it is an essential relationship - for us and for the world."
They also referred to the "Arab Spring", promising not to abandon protesters fighting for democracy across the Arab world.
"We will not stand by as their aspirations get crushed in a hail of bombs, bullets and mortar fire," they wrote.
The role of NATO in Libya and the Western response to the uprisings are expected to be the focus of talks between the two leaders later this week.
The two are also expected to announce the formation of a US-British national security council to work together on international challenges and share intelligence, an Obama administration official said.
It was not developed in response to any one issue, but will help enable "a more guided, coordinated approach to analyse the 'over the horizon' challenges we may face in the future."
At a lavish banquet at Buckingham Palace, Obama raised a toast to Queen Elizabeth II and the vitality of the special relationship between the US and Britain.
The president said the queen is a living witness to the power of the alliance between the two countries.
He also thanked Britain for supporting US efforts in Iraq and Afghanistan, and acknowledged the sacrifices the British people have endured in order to do so.
Earlier, Obama and his wife Michelle met Prince William and his new bride, Catherine, at a formal ceremony at the palace.
The royal newlyweds greeted the Obamas in the grand 1844 room the palace after making a special trip to London.
It was the first time Catherine, the Duchess of Cambridge, had undertaken a role as a member of the royal family since her wedding on April 29.
Obama also joined Prince Philip to conduct a ceremonial review of a Scots Guard regiment on the palace grounds.
The president spoke of how his country was fascinated by the royal wedding when he met Prince Charles, William's father and heir to the throne, at the White House in Washington a few weeks ago.
Obama is only the second US president to be honoured with a state visit by the queen
The US leader is in Britain as part of a six-day European tour, which began on Monday in Ireland.
There he visited the small town of Moneygall, to the delight of the local residents, where his maternal great-great-great grandfather lived.
The US leader had to leave Ireland early on Monday because of an ash cloud from an Iceland volcano, which has disrupted flights over the British Isles.
Source: Al Jazeera and agencies