US President Donald Trump has celebrated his 80th birthday with an extraordinary display of political machismo, staging a cage fight on the White House lawn hours after announcing a peace deal with Iran.

In unprecedented scenes, Trump walked out of the Oval Office alongside Ultimate Fighting Championship (UFC) boss Dana White and headed towards the giant arena dubbed "The Claw."

On the way, the president mounted the historic Truman balcony and saluted while the national anthem and 12 US military jets staged a noisy flyover of the White House.

Trump then took his place on the South Lawn, beside the mesh-fenced cage called the Octagon, where 14 fighters competed in the first professional sporting event ever held at the White House.

He was cageside as the first fighter, Brazil's Diego Lopes, won by a knockout.

Fans rally behind White House

Fans gathered to watch the extravaganza on a giant screen on the Ellipse outside the White House, defending the event.

Trump, who has deep ties with the sport, has defended the UFC event as a unique spectacle.

"This is going to be an event you're really gonna like," Trump said as he hosted some of the fighters in the Oval Office in May.

The White House says the UFC is bearing the entire cost.

Sponsors, including Bud Light and Polymarket, had their logos emblazoned on the Octagon, with the broadcast handled exclusively by Paramount.

For his last birthday, Trump oversaw a military parade in Washington, marking the 250th anniversary of the US Army.