PARIS: World leaders lined up to pay tribute to US President Joe Biden Sunday after he announced he was dropping out of the US presidential race.

Biden notified the public of his decision in a letter, a stunning move that upends the 2024 race for the White House. He endorsed Vice President Kamala Harris as the Democratic Party's new nominee.

"You've taken many difficult decisions thanks to which Poland, America and the world are safer, and democracy stronger," said Polish Prime Minister Donald Tusk.

"I know you were driven by the same motivations when announcing your final decision. Probably the most difficult one in your life," added Tusk, who served as the European Council president between 2014 and 2019.

UK Prime Minister Keir Starmer said he respected Biden's decision, adding: "I look forward to us working together during the remainder of his presidency.

"I know that, as he has done throughout his remarkable career, he will have made his decision based on what he believes is best for the American people," he wrote on X, formerly Twitter.

German Chancellor Olaf Scholz also paid tribute to Biden's legacy.

"My friend @POTUS Joe Biden has achieved a lot: for his country, for Europe, for the world," he wrote on X. "His decision not to run again deserves respect."

Israel's Defence Minister Yoav Gallant thanked Biden for his "unwavering support of Israel over the years."

Writing on X, he added: "Your steadfast backing, especially during the war, has been invaluable. We are grateful for your leadership and friendship."

Israeli President Isaac Herzog, whose role is largely ceremonial, also thanked Biden for his "steadfast support for the Israeli people over his decades long career", in a post on X.

Canadian Prime Minister Justin Trudeau also thanked Biden for his years of service.

"I've known President Biden for years," he wrote on X.

"He's a great man, and everything he does is guided by his love for his country. As President, he is a partner to Canadians - and a true friend. To President Biden and the First Lady: thank you."

Australian Prime Minister Anthony Albanese wrote on X: "Thank you for your leadership and ongoing service President Biden."

"The Australia-US Alliance has never been stronger with our shared commitment to democratic values, international security, economic prosperity and climate action for this and future generations."

Former president Barack Obama, with whom Biden served two terms as vice president, praised his record in office.

"Internationally, he restored America's standing in the world, revitalized NATO, and mobilized the world to stand up against Russian aggression in Ukraine," he said.

While he had every right to run for reelection, Biden's decision to drop out of the race was testament to his "love of country", Obama added.

The Kremlin said it was monitoring developments.

"The election is still four months away. And it's a long time, during which a lot can change. We need to pay attention, follow what will happen and go about our business," Kremlin spokesman Dmitry Peskov told the Life.ru news outlet.

Even as world leaders paid tribute to his performance on the world stage, leading Republicans were insisting he was unfit to remain president.

"If Joe Biden is not fit to run for president, he is not fit to serve as president," said a statement from House Speaker Mike Johnson, the top Republican in Congress.

"He must resign the office immediately. November 5 cannot arrive soon enough," he added.

Former president Donald Trump, who is running for the presidency again, wrote on his Truth Social network: "Crooked Joe Biden was not fit to run for President, and is certainly not fit to serve."

 -AFP