US President George W Bush has signed a book of condolence for the victims of Thursday's London bombings.
Mr Bush went straight to the UK embassy on his return from the G8
The ceremony took place at the UK embassy in Washington, where the president went on his return from the G8 summit in Scotland.
He praised the "great spirit of Londoners and the people of Great Britain" and laid a wreath.
The UK Ambassador to the US, Sir David Manning, told Mr Bush that his gesture was "hugely appreciated".
"We have had the most wonderful gestures of support from the Americans over the last 36 hours," the ambassador said.
"It's a huge source of comfort," he added.
Mr Bush said: "The people of Great Britain can know the American people stand in solidarity with them".
Vice-President Dick Cheney also called at the embassy to deliver his condolences.
Earlier on Friday, New York Mayor Michael Bloomberg signed a condolence book at the British consulate in New York.
"All New Yorkers' prayers are with our friends in Britain," he wrote.
More than 50 people died and about 700 were wounded in Thursday's blasts, targeting public transport in London.
Emergency workers are still trying to remove bodies from an Underground train wrecked in the worst explosion.