A US government watchdog is investigating whether Donald Trump broke federal law by using the White House as a campaign command centre.
The US Office of Special Counsel will probe the Trump campaign's use of Government property as an election day "war room", according to Democratic Representative Bill Pascrell.
In a statement, Pascrell said the federal watchdog responded on Thursday to his call for a probe, telling him a special unit "has opened an investigation into these allegations to determine if the Hatch Act was violated."
President Donald Trump monitored election returns in the living room of the White House residence on Tuesday, later addressing some 200 supporters gathered in the East Room.
Pascrell had asked the special counsel, Henry Kerner, to investigate reports suggesting that Trump used space in the adjacent Eisenhower Executive Office Building - on the grounds of the White House - as a campaign "war room."
The New Jersey lawmaker said Trump was also expected to be briefed in the White House residence and the Oval Office throughout the day by campaign officials, which he said put executive branch officials at risk of violating federal law.
The Hatch Act of 1939 limits the political activities of federal employees, except the president and vice president.
The White House denied any violation of the federal law.
"Both the official activity of Administration officials, as well as any political activity undertaken by members of the Administration, are conducted in compliance with the Hatch Act," said spokesman Judd Deere.
No comment was immediately available from the Office of the Special Counsel.
Pascrell said the Special Counsel's office told him it "was not consulted (by the Trump campaign or White House) on the decision to use space inside the Eisenhower Executive Office Building as a campaign `war room.'''
The agency launched an investigation last month of Secretary of State Mike Pompeo's speech to the Republican National Convention in August, and last year recommended the firing of then-senior Trump adviser Kellyanne Conway for repeated violations.
Kerner is a Trump appointee who previously worked for Republican lawmakers in Congress. His office is an independent agency that enforces the Hatch Act. It is not connected to the office of former U.S. Special Counsel Robert Mueller.
