A US judge has halted construction of the above ground portion of President Donald Trump’s White House ballroom project, but has allowed plans for an underground bunker to proceed.

Judge Richard Leon wrote in his ruling on Thursday that Congress must approve the project, adding that Trump appeared to be trying to side-step a previous court order by reclassifying the ballroom plans as vital for national security.

“National security is not a blank cheque to proceed with otherwise unlawful activity,” the judge wrote.