Barack Obama tweeted his tributes to the London attack victims
The former US President, tweeted at 1pm GMT: "My heart goes out to the victims and their families in London.
"No act of terror can shake the strength and resilience of our British ally."
Within 20 minutes his tweet had garnered 36,000 'likes' and 8,900 'retweets'.
It is not known where Mr Obama was tweeting from, although he was last seen in New York City on March 10.
The Democrat's message was miles apart from his sucessor Donald Trump, who last night tweeted Theresa May is "doing very well".
Mr Trump, said: "Spoke to UK Prime Minister Theresa May today to offer condolences on the terrorist attack in London.
"She is strong and doing very well."
Just before 2.45pm on Wednesday terror struck at the heart of democracy as the attacker drove his rented Hyundai 4×4 along the pavement on the west side of Westminster Bridge, knocking down unsuspecting tourists, students and workers on the busy bridge.
Spanish teacher Aysha Frade was killed on Westminster Bridge by the attacker
He then drove the car into the railings on the edge of the ground of the Palace of Westminster then ran through the gates into New Palace Yard wielding what has been described as a machete-like knife.
He was seen repeatedly stabbing PC Keith Palmer who attempted to stop him and was then shot by armed officers.
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American Kurt Cochran was also killed on Westminster Bridge
Police and paramedics rushed to the scene where they desperately tried to save all the injured, including the attacker.
MP Tobias Ellwood, a former Army captain, rushed to give CPR to the injured policeman who later died.
This morning a statement by the Met Police revealed four people had died, including a man in his mid 50s and a Spanish woman in her mid 40s named as Aysha Frade by Spanish press.
Acting lead commissioner Mark Rowley said 29 people had been injured, with seven still in critical condition.
He branded the incident as “international terrorism” and said six addresses in London and Birmingham had been searched.
Seven people have been arrested, he added.