"Bad deal", Trump said, adding "wanted me to cut ribbon - NO!"
Kahn even questioned Britain's Prime Minister Theresa May's urgency to extend an invitation of a state visit to Trump in the first place.
The embassy move is, in fact, the result of a decade-long project initiated by the administration of former Republican president George W. Bush.
In Washington, White House spokeswoman Sarah Huckabee Sanders said Trump's comment was exclusively about an embassy-related visit.
The President is also due to meet the Queen in a full state visit at a later date but a source claimed the lack of "bells and whistles" may have put him off coming on the initial visit.
Downing Street has accused Jeremy Corbyn and Sadiq Khan of jeopardising relations with America for telling Donald Trump he is not welcome in Britain, after the USA president called off a planned visit to London in the face of likely mass protests.
While the embassy statement emphasized that the U.S. was able to erect a new building project through a property swap, without using taxpayer funds, Trump might have a point on the economics of selling the old embassy in London's tony Mayfair district.
Simon Dawson Reuters
There is likely some relief in the British government at Trump's decision, which would have caused at the very least a major policing operation.
When the PM visited the White House, she was pictured holding hands with the president.
May and Trump fell out in November over his retweeting of anti-Muslim videos posted online by the deputy leader of the far-right Britain First group, Jayda Fransen. He said his countrymen love and admire America and Americans but find Trump's policies polar opposite to the city's values, Khan said in a statement released on Twitter on Friday.
There has been speculation that his visit would result in mass protests, so people have been responding online with their own very serious reasons for not visiting London.
The British government said the opening of the embassy was a matter for the United States.
Mr Johnson tweeted at about 11am: "The US is the biggest single investor in the United Kingdom - yet Khan & Corbyn seem determined to put this crucial relationship at risk. But maybe Sadiq Khan, Jeremy Corbyn and the Labour Party planning mass protests, maybe those optics he didn't like the look of".