WASHINGTON, United States (AFP) — Donald Trump celebrates his 80th birthday in typically forceful style on Sunday, as the oldest US president ever to take office holds a bloody cage match on the White House lawn.

The unprecedented "UFC Freedom 250" event will see 14 Ultimate Fighting Championship stars beat each other to a pulp in a giant arena called The Claw.

Costing $60 million, it's linked to this year's festivities for the 250th anniversary of US independence — but it also happens to fall on the day that Trump enters his ninth decade.

Critics have derided the violent extravaganza in America's most famous backyard, saying it is in poor taste during a war with Iran that has sent prices soaring for ordinary people.

Trump may clinch a long-sought peace deal with Iran on his big day, although Tehran has cast doubt on that timing.

The billionaire president — who has deep ties with a sport whose young male fans reflect his own political base — 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 muscle-bound, bare-knuckle fighters in the Oval Office in May.

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

UFC chief content officer Craig Borsari denied blending sport with politics.

"The way we look at this is we have an unbelievable, incredibly unique opportunity to celebrate this country and our athletes," Borsari told a news conference this week.