Lawyers representing the US federal government argued that a court could not stop construction of a White House ballroom because it was already underway and because of the sensitive security concerns they say the structure is meant to address.

Attorney Yaakov Roth, speaking during an exchange with US Appeals Court Judge Patricia Millett, said only Congress could halt the $400-million project. The administration has been asking the court to allow it to press on with the ballroom without congressional approval.