The billion-dollar embassy moved from its long-standing site in Grosvenor Square, central London, to its new home at Nine Elms, south of the city, in January.
But during a rally in Michigan on Saturday, Trump criticized the move. "We had the best site in all of London," he told supporters, before adding that now, "We have an embassy in a lousy location."
Trump told the rally that the previous site in Grosvenor Square was "sold for like 250 million" -- but that organizers "spent all of that money, plus a lot more, to build a new embassy in a lousy location."
His comments come ahead of a planned visit
to the UK on July 13, Trump's first trip to Britain since becoming President, the White House and Downing Street announced last week.
It will not be a state visit -- a move welcomed by London Mayor Sadiq Khan, who told British talk show host Robert Peston on Sunday that he was glad "the red carpet will not be rolled out" for Trump.
Trump and Khan have frequently traded barbs in the past, notably when the US President appeared to misconstrue a statement by the mayor in response to a terror attack in London last year.
Trump's visit follows months of back-and-forth negotiations over the trip, with Trump canceling a previous visit to London in January to officially open the new embassy.
"I was supposed to cut the ribbon," said Trump at Saturday's rally, before blaming the embassy deal on the Obama and Bush administrations.
In fact, the decision to move out of the Grosvenor Square building
in the high-end Mayfair district was taken under the Bush administration in 2008, principally because the building was proving harder to secure in an age of terrorist threats -- and also, in small part at least, because the US government did not wholly own it.
British property law historically allows the ground underneath buildings to be held by people and entities other than the owners of the bricks and mortar above. In this case, the land is owned by the Duke of Westminster, whose property empire controls much of the land in central London, and is leased back to the US at a nominal -- or "peppercorn" -- rent.
"We looked at all our options, including renovation of our current building on Grosvenor Square," then-Ambassador Robert Tuttle said.
"In the end, we realized that the goal of a modern, secure and environmentally sustainable embassy could best be met by constructing a new facility."
The historic Mayfair site is now set to be converted into a luxury hotel by Qatari investors.
From concrete to glass
The new embassy is a world away from its former concrete home, which was designed by Finnish-American modernist architect Eero Saarinen.
The 12-storey glass cube occupies an almost five-acre site, in a former industrial area south of the River Thames.
Security requirements are tight -- it is set back 100 feet from the street and boasts a semi-circular pond as a security measure.
Designed by Philadelphia architecture firm KieranTimberlake, the embassy houses around 800 staff and is expected to receive 1,000 visitors daily.