The U.S. Justice Department has again asked a federal judge to lift an injunction ​holding up progress on President Donald Trump's ballroom project, saying ‌Saturday's shooting outside the White House showed an urgent need for improved security.

The Justice Department, in a five-page court filing on Sunday, said the incident underscores the critical need for "top-level, state-of-the-art security at ​the White House, including the ballroom," adding that it is vital to national security. It also asks that the lawsuit challenging the project be dismissed.

The court filing stated: "This is a terrible, ​tremendously harmful case to the United States of America, and all it stands for!"

U.S. District Judge Richard Leon, an appointee of former President George W. Bush sitting ​in Washington, ruled in April that Trump lacked legal authority to ​build the ballroom without congressional approval.

Leon issued an injunction that halted "above-ground construction ‌of ⁠the planned ballroom," but his order was quickly put on hold by an appeals court. Construction has continued.

The DOJ had previously asked Leon to dissolve his injunction and throw out the lawsuit over the ballroom after ​a foiled attack at ​the White ⁠House Correspondents' Association dinner in April. Leon has not acted on that request.

The lawsuit was filed by ​the National Trust for Historic Preservation, a congressionally chartered ​nonprofit organisation. ⁠It said it would not drop its lawsuit after the April attack, despite the Justice Department's request.

The gunman who fired at a ⁠White House ​checkpoint on Saturday was shot by officers ​and died after being taken to the hospital on Saturday evening, the Secret Service ​said.