LONDON (Reuters) - The U.S. Embassy in London moves next month to a new billion-dollar home overlooking the River Thames -- just as U.S. President Donald Trump’s actions have placed strains on the “special relationship” between Britain and the United States.

Slideshow ( 15 images )

Britain’s closest ally will leave behind an imposing 1960 stone and concrete embassy in London’s upmarket Grosvenor Square -- an area known as ‘Little America’ during World War Two, when the square also housed the military headquarters of General Dwight D. Eisenhower.

The old embassy was also a focus for British discontent with U.S. policy. Anti-Vietnam War protests in the 1960s drew thousand of Britons, including celebrities of the day like Rolling Stones frontman Mick Jagger.

The new 12-storey building on the south bank of the river is at the heart of a huge regeneration project in a former industrial zone known as “Nine Elms”. Set in what will become an urban park, it will open for business on Jan. 16, hosting 800 staff and about 1,000 visitors each day.

“This embassy, when you look out through the windows, it reflects the global outlook of the U.S. going forward in the 21st century: rather looking out, than looking in,” said Woody Johnson, Trump’s appointed U.S. ambassador to Britain.

The U.S. State Department ran a competition to design the new building in 2008. Its $1 billion construction was wholly funded by the sale of other properties in London.

The glass structure “gives form to core democratic values of transparency, openness and equality” a State Department briefing document said. Inside the cube, visitors will be greeted by an imposing stone facade featuring the bald eagle of the United States’ Great Seal.

The embassy is also designed to exacting security specifications, set back at least 100 feet (30 meters) from surrounding buildings - mostly newly-erected high-rise residential blocks - and incorporating living quarters for the U.S. Marines permanently stationed inside.

“This isn’t just a new office, though, it signifies a new era of friendship between out two countries. President Trump wants us to work more closely than ever with the UK,” Johnson said.

The British relationship with its former colony is a broad political, cultural and military alliance forged over the last century and exercised on battlefields around the world. But it has been tested in recent months.

Prime Minister Theresa May was the first foreign leader to visit the White House after Trump’s surprise election in November 2016 and used the trip to invite him for a full state visit.

While the two leaders have committed to strengthen trade links and have spoken regularly, their governments have disagreed on several issues, such as Trump’s decision to decertify Iran’s compliance with a multilateral nuclear deal, and his move to recognize Jerusalem as the capital of Israel.

A possible state visit by Trump remains a contentious issue among Britons, with lawmakers and campaign groups calling for the offer to be rescinded and promising to take to the streets in protest if he does come to Britain.

“The right to protest is a basic right in this country and our country. Expressing one’s view is well within the bounds of reasonableness,” Johnson said.

He said he hoped Trump could attend an as-yet unscheduled opening ceremony for the new building but that there were no firm plans in place.

This month, May publicly criticized Trump for reposting British far-right anti-Islam videos from his Twitter accounts. He responded with a rebuke, telling May to focus on Islamic extremism in Britain.