A US judge has temporarily halted President Donald Trump's White House ballroom construction project, ruling that proper procedures were not followed before the project began.

The decision comes after the White House was sued by the National Trust for Historic Preservation.

"I have concluded that the National Trust is likely to succeed on the merits because no statute comes close to giving the President the authority he claims to have," said Judge Richard Leon.

Trump criticised the ruling on his social media platform, saying the project is going well, and "will be the finest Building of its kind anywhere in the World".

The Trump administration previously said its plan was more economical than renovating the East Wing. It also noted that many presidents made changes to the White House.

Leon's ruling, published on Tuesday, continued: "The President of the United States is the steward of the White House for future generations of First Families. He is not, however, the owner!"

"(U)nless and until Congress blesses this project through statutory authorisation, construction has to stop!" added the judge, who was appointed by President George W Bush.

The 35-page ruling uses many exclamation points, arguing that Congress must approve for the project to resume.

The order takes effect in 14 days, allowing a possible appeal.

In the lawsuit, the preservation group argued that the White House broke the law by beginning construction without filing plans with the National Capital Planning Commission, by not seeking an environmental assessment of the project, and by declining to seek authorisation from Congress.

It also alleged Trump was violating the US Constitution, "which reserves to Congress the right to dispose of and make all rules regarding property belonging to the United States".

In his conclusion, Leon wrote that with White House approval from Congress, "the American people will benefit from the branches of Government exercising their constitutionally prescribed roles".

"Not a bad outcome, that!"

The East Wing, constructed in 1902, was demolished in October to make way for Trump's multi-million-dollar ballroom.

Since then, the proposed blueprint has expanded from a ballroom with a capacity of 500 people to a space that can fit 1,350 guests.

The White House says the project is expected to cost $400m (£302m) and is being funded entirely by private donors.

The National Trust is a nonprofit organisation tasked by the US Congress with helping preserve historic sites.

The group's president, Carol Quillen, released a statement, saying: "We are pleased with Judge Leon's ruling today to order a halt to any further ballroom construction until the Administration complies with the law and obtains express authorization to go forward.

"This is a win for the American people on a project that forever impacts one of the most beloved and iconic places in our nation."

Reacting to the judge's decision, Trump wrote on his Truth Social account: "The National Trust for Historic Preservation sues me for a Ballroom that is under budget, ahead of schedule, being built at no cost to the Taxpayer, and will be the finest Building of its kind anywhere in the World."

He also criticised the trust for suing to stop his renovation of the Kennedy Center, which Trump recently renamed after himself.

"All I am doing is fixing, cleaning, running, and 'sprucing up' a terribly maintained, for many years, Building," Trump wrote about the performing arts venue in Washington DC.

In later remarks with reporters, Trump said the White House would appeal against the ruling, and denied that he needs approval from Congress to continue building.

He also noted King Charles III's forthcoming visit to the US, saying that a ballroom tent is insufficient to host him because the grass can get very wet when it rains.

"King Charles, who's a great guy. We don't want him to sit in a pool of water," he said.

When asked for comment, the White House directed the BBC to Trump's post.

Construction is already well underway, after the East Room was torn down in a matter of days last autumn.

Demolition and foundation work have already been completed; aboveground construction is scheduled to begin next month.