US President Joe Biden has announced that he will end his candidacy for re-election, saying "it is in the best interest of my party and the country".

It comes four months before Americans go to the polls, upending the race for the White House.

It follows weeks of intense pressure from fellow Democrats after a faltering debate performance against Republican Donald Trump at the end of June.

Following the announcement on Sunday evening, President Biden gave his endorsement in the presidential race to Vice President Kamala Harris.

In a letter posted to his social media account, he said it had been the greatest honour of his life to serve as president.

• LIVE UPDATES: Joe Biden withdraws from US presidential race

"And while it has been my intention to seek reelection, 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 wrote in his statement.

Calls for Biden to withdraw from the race began to grow after a disastrous debate performance in late June against Donald Trump.

During the debate he was criticised for often being incoherent and speaking in a weak voice - something which his party claimed as down to a cold.

Following it, there were growing calls from within his own party for him to stand aside, with a growing number of congressional Democrats worried his campaign would hurt their own re-election chances in November.

A handful of senators, who sit in the upper chamber of Congress, also called for him to withdraw.

While Kamala Harris has the backing of the current president, it is unclear at the moment if she will be selected unopposed as the new candidate.

The focus will now be on the Democratic National Convention which takes place next month in Chicago.

It begins on 19 August - but Mr Biden's party had sped up the process to comply with a 7 August candidate certification deadline in the state of Ohio - meaning the new nominee should be confirmed in just over two weeks.

'Heartfelt appreciation'

In his statement, President Biden thanked his Vice President Kamala Harris, saying she was an "extraordinary partner".

"And let me express my heartfelt appreciation for the American people for the faith and trust you have placed in me," his statement added.

"I believe today and 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."

He wrote that he would address the nation on the matter next week.

Last week he returned to his home in Delaware after being diagnosed with Covid, but said on Friday he was looking forward to "getting back on the campaign trail next week".

He has previously said only the "Lord Almighty" could make him withdraw, but then later said he would consider withdrawing if he had a health condition.

Responding on his Truth Social platform, Republican nominee Donald Trump said that Joe Biden was "was not fit to run for President".