US President Joe Biden said it was “the greatest honor of my life” to serve as he ended his campaign

US President Joe Biden has announced he will end his re-election bid, saying “it is in the best interests of my party and the country”.

The event took place four months before Americans went to the polls, upending the race for the White House.

The move comes after weeks of intense pressure from other Democrats following an unconvincing debate performance with Republican candidate Donald Trump in late June.

Following the announcement Sunday evening, President Biden expressed his support for Vice President Kamala Harris in the presidential race.

In his endorsement, he said his “first decision as the party’s candidate in 2020” was to choose Ms Harris, saying “it was the best decision I ever made”.

In a letter posted on his social media account announcing his resignation, he said being president was the greatest honor of his life.

“While I intend to seek re-election, I believe it is in the best interests of the party and the country to step down and focus on fulfilling the duties of the President for the remainder of my term,” he wrote in his statement.

Calls for Biden to drop out of the race began to mount after his disastrous debate performance in late June with Donald Trump.

During the debate, he was criticised for often being incoherent and speaking in a weak voice – which his party attributed to a cold.

There have since been growing calls from within his own party for him to resign, as a growing number of Democrats in Congress fear his campaign will harm their re-election chances in November.

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

Less than two weeks ago, President Biden hosted a summit with NATO leaders, knowing he would face close scrutiny after his debate performance.

The event did not ease tensions within his own party, with Mr. mistakenly called Ukrainian President Volodymyr Zelensky “President Putin”and appeared to refer to the vice president as “Vice President Trump.”

While Kamala Harris has the support of the current president, it is currently unclear whether she will be selected unopposed as the new nominee.

After he withdrew on Sunday evening, the BBC’s US partner network CBS reported that the Democratic National Committee had held an emergency meeting.

The focus now is on the Democratic National Convention taking place next month in Chicago.

Biden won the primaries by a landslide, meaning delegates representing each state at the convention were pledged to vote for him — although they will now presumably be exempt from voting for another candidate.

In his statement, President Biden thanked Vice President Kamala Harris, saying she has been an “extraordinary partner.”

“I would like to express my sincerest gratitude to the American people for the faith and trust you have placed in me,” he added in the statement.

“I believe today and I will always believe: there is nothing that America cannot do – when we work together. We need only remember that we are the United States of America.”

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

He returned home to Delaware last week after being diagnosed with Covid, but said on Friday he looked forward to “being back on the campaign trail next week.”

He had previously said that only “Almighty God” could make him withdraw, but later said he would consider withdrawing if he had health problems.

Responding on his Truth Social platform, Republican candidate Donald Trump said Joe Biden is “not qualified to run for president.”