Donald Trump says he would like to see Boris Johnson and Nigel Farage "come together" and unite ahead of Britains snap general election in order to see a better UK-US trade deal post-Brexit.

Speaking to reporters at the White House, the US president said that both the UK prime minister and the Brexit Party leader were his friends, but that Johnson was "the right man for the time."

He said: "I like them both. I think Boris will get it right. They're both friends of mine. What I'd like to see is for Nigel and Boris to come together. I think that's a possibility."

The 73-year-old went on to encourage a structured UK-EU divorce in order to facilitate continued trade between the UK and the US.

"We're far and away the number one economy in the world, and if you do [Brexit] a certain way, we're prohibited from trading with the UK," he said.

"That would be very bad for the UK because we can do much more business [than the] European Union."

Trump first waded into the UK's snap election last week, telling Farage in a radio interview that the leader of the opposition Labour Party, Jeremy Corbyn, would be "so bad" for Britain if he wins.

He also floated the idea that Johnson and Farage should combine forces, saying it could be "terrific."

"If you and he get together it's, you know, unstoppable force," Trump told Farage in the interview.

Farage responded by saying he would be "right behind" Johnson on the condition that the prime minister drop his Brexit deal and opts instead for "clean break" no-deal scenario.

Meanwhile on Sunday, Farage said he would not run for a seat in parliament in the UK's snap election on December 12, and would instead focus on campaigning against Johnson's EU divorce deal.

The election was called because of an impasse in parliament over Brexit, more than three years after voters decided to leave the bloc.