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The US president also attacked the European Union over trade, threatening to "take on" the bloc which he said was "formed to take advantage of the US".
In wide-ranging remarks during a campaign-style rally in Michigan, Mr Trump said a meeting with North Korea could happen over the next three to four weeks.
His comments followed a phone call late on Saturday with South Korean president Moon Jae-in, during which both leaders agreed on the need for an early summit with Kim Jong-un and discussed possible locations for the summit, rumoured to be Singapore or Mongolia.
Mr Trump's remarks on the location of the US embassy in London follow three months after he cancelled a scheduled trip to the British capital blaming the Obama administration for building the new embassy in an "off location".
Reason I canceled my trip to London is that I am not a big fan of the Obama Administration having sold perhaps the best located and finest embassy in London for “peanuts,” only to build a new one in an off location for 1.2 billion dollars. Bad deal. Wanted me to cut ribbon-NO!
— Donald J. Trump (@realDonaldTrump) January 12, 2018
Speaking at Saturday's rally, the US president, who is visiting the UK on 13 July, lashed out again at the move from Grosvenor Square in the centre of the capital to a new location south of the Thames.
Mr Trump told a crowd of supporters the Nine Elms site was in a "lousy" and "horrible" location and cost too much.
"In the UK, in London, we had the best site in all of London. The best site. Well, some genius said, we're gonna sell the site and then we're going to take the money and build a new embassy..." he said.
"They go out and they buy a horrible location. And they build a new embassy. That's the good news. The bad news is it cost over a billion dollars."
Mr Trump blamed his predecessors for the project, calling it a "Bush-Obama special", adding later: "Hopefully we'll have many years of success with that embassy."
The US announced plans to move to the new site in October 2008 - when George W Bush was in the White House.
On Thursday, Downing Street confirmed Mr Trump would conduct his first presidential visit to the UK in July.
The long-awaited trip — following months of speculation over a potential date — is expected to be a “working visit” rather than a full-blown state occasion.
Announcing the contentious plans, Sir Kim Darroch, the the UK’s ambassador to the US, said he was “delighted” that Mr Trump will visit the UK.
On the subject of trade, Mr Trump said the EU "sounds so nice" but was "formed to take advantage of the US".
He said he did "not blame them [the EU]. I blame past presidents", adding: "Long-term you're going to be so happy... or we are not doing business with these guys."