Barack Obama arrived at Downing Street for talks with David Cameron, amid controversy over the US President's forthright support for Britain's continued membership of the EU.
Mr Obama, who earlier enjoyed lunch with the Queen at Windsor Castle, used a newspaper article to argue that EU membership "magnified" the UK's status on the global stage.
His intervention in the bitter EU referendum debate led to claims of hypocrisy from Brexit campaigners, who had urged him to "butt out" of the UK's decision on June 23.
Writing in the Daily Telegraph, the president highlighted the special relationship between his country and the UK "forged as we spilled blood together on the battlefield".
Mr Obama was greeted with a warm handshake from Mr Cameron as he arrived in Downing Street in his armoured limousine - nicknamed "the beast".
The two leaders smiled and waved to photographers on the doorstep of Number 10, but did not respond to reporters' questions about the strength of the US-UK special relationship.