The Prime Minister has praised Joe Biden for making a decision based on what he believed to be in “the best interest of the American people” after the US president withdrew his bid for re-election.

Mr Biden said on Sunday that it was “in the best interest of my party and the country for me to stand down”.

Responding to Mr Biden’s decision, Sir Keir Starmer said: “I respect President Biden’s decision and I look forward to us working together during the remainder of his presidency.

“I know that, as he has done throughout his remarkable career, President Biden will have made his decision based on what he believes is in the best interests of the American people.”

Mr Biden has also offered his “full support” to Vice President Kamala Harris to be the Democrat nominee.

In a post on his social media account, he said: “My fellow Democrats, I have decided not to accept the nomination and to focus all my energies on my duties as President for the remainder of my term.

“My very first decision as the party nominee in 2020 was to pick Kamala Harris as my Vice President. And it’s been the best decision I’ve made. Today I want to offer my full support and endorsement for Kamala to be the nominee of our party this year. Democrats — it’s time to come together and beat Trump. Let’s do this.”

In a separate letter posted to X, Mr Biden said it had been the greatest honour of his life to serve as president.

“And while it has been my intention to seek re-election, I believe it is in the best interest of my party and the country for me to stand down and to focus solely on fulfilling the duties as President for the remainder of my term.”

He said in his statement he would address the nation on the matter next week, adding: “For now, let me express my deepest gratitude to all those who have worked so hard to see me reelected. I want to thank Vice President Kamala Harris for being an extraordinary partner in all this work. And let me express my heartfelt appreciation to the American people for the faith and trust you have placed in me.

“I believe today what I always have: that there is nothing America can’t do – when we do it together. We just have to remember we are the United States of America.”

The decision comes after escalating pressure from Mr Biden’s Democratic allies to step aside following his faltering June 27 debate.

Mr Biden’s term in office ends at noon on January 20 2025.

Vice President Kamala Harris said she was “honoured” to have the endorsement of Joe Biden.

In a statement, she thanked the US president for his “extraordinary leadership” and for making a “selfless and patriotic act” by stepping aside.

She said: “I am honoured to have the president’s endorsement, and my intention is to earn and win this nomination.”

She added: “I will do everything in my power to unite the Democratic Party —and unite our nation — to defeat Donald Trump and his extreme Project 2025 agenda.

“We have 107 days until Election Day. Together, we will fight. And together, we will win.”

Former Prime Minister Rishi Sunak praised Joe Biden’s “love for America and dedication to service”.

In a post on X, formerly Twitter, the former prime minister said: “Working with Joe Biden, I saw firsthand his love for America and dedication to service.

“Our partnership has led to significant achievements, including Aukus, steadfast support for Israel and joint efforts in defending our people from Houthi threats.

“I wish him all the best.”

Writing on his Truth Social platform, former US president Donald Trump, who is standing for the Republican Party, said: “Joe Biden was not fit to run for President, and is certainly not fit to serve – And never was!”

He added: “We will suffer greatly because of his presidency, but we will remedy the damage he has done very quickly. MAKE AMERICA GREAT AGAIN!”

Former president Barack Obama praised Mr Biden as a “patriot of the highest order”, saying the US president had put American interests ahead of his own as he decided not to seek re-election.

In both a personal and political statement, he said he and his wife Michelle wanted to thank “Joe and Jill for leading us so ably and courageously during these perilous times”.

He added that Mr Biden has a “fundamental decency and belief that everyone counts”.

He admitted the Democratic Party would be “navigating uncharted waters in the days ahead” and stopped short of endorsing Ms Harris as Mr Biden and other senior Democrats have.

He continued: “But I have extraordinary confidence that the leaders of our party will be able to create a process from which an outstanding nominee emerges.”

Ukrainian President Volodymyr Zelensky said the country of Ukraine was “grateful to President Biden for his unwavering support for Ukraine’s fight for freedom, which, along with strong bipartisan support in the United States, has been and continues to be critical”.

He said in a post on X: “Many strong decisions have been made in recent years and they will be remembered as bold steps taken by President Biden in response to challenging times. And we respect today’s tough but strong decision.

“We will always be thankful for President Biden’s leadership. He supported our country during the most dramatic moment in history, assisted us in preventing Putin from occupying our country, and has continued to support us throughout this terrible war.

“The current situation in Ukraine and all of Europe is no less challenging, and we sincerely hope that America’s continued strong leadership will prevent Russian evil from succeeding or making its aggression pay off.”

In response to Mr Biden’s statement, Reform UK leader Nigel Farage said: “I predicted this would happen in September 2023.

“Whoever they pick, Trump will win in November.”