U.S. President Joe Biden mispronounced the name of former U.K. Treasury chief Rishi Sunak while congratulating him on his appointment as head of government, The Telegraph reported.

But he stumbled over his British counterpart's name, calling him "Rashee Sanook".

The US President said: "And whether it's the United Kingdom, where just today, we've got news that Rishi Sunak is now the prime minister. As my brother would say, 'go figure'," Mr Biden said.

"And the Conservative Party, expected to become the Prime Minister, I think, tomorrow when he goes to see the King.

"Pretty astounding. A groundbreaking milestone. And it matters, it matters."

On Monday, Rishi Sunak was elected head of the ruling Conservative Party in Britain, and he will also take over as prime minister of the country. Sunak will become Britain's third prime minister this year.