World leaders said they were looking forward to working with Joe Biden, the Democrat sworn in as US president on Wednesday after four turbulent years under Donald Trump.

Charles Michel, president of the European Council, tweeted congratulations to Biden and Vice President Kamala Harris, adding: "It's time to bring back conviction & common sense and rejuvenate our EU-US relationship."

European Commission President Ursula von der Leyen said: "Europe is ready for a fresh start."

President Hassan Rouhani hailed the departure of "tyrant" Trump, Tehran having repeatedly called on Washington to lift sanctions imposed over its nuclear drive.

"We expect (the Biden administration) to return to law and to commitments, and try in the next four years, if they can, to remove the stains of the past four years," said Rouhani.

Biden's administration wants the United States back in the landmark Iran nuclear accord, from which Trump withdrew, provided Tehran returns to strict compliance.

Prime Minister Benjamin Netanyahu urged Biden to strengthen the long-standing alliance between the two countries.

"I look forward to working with you to further strengthen the US-Israel alliance, to continue expanding peace between Israel and the Arab world and to confront common challenges, chief among them the threat posed by Iran," Netanyahu said in a video.

"The bond between North America and Europe is the bedrock of our security, and a strong NATO is good for both North America and Europe," said NATO General Secretary Jens Stoltenberg.

"NATO Allies need to stand together to address the security consequences of the rise of China, the threat of terrorism, including in Afghanistan and Iraq, and a more assertive Russia."

Pope Francis urged Biden to promote "reconciliation and peace" around the world.

"At a time when the grave crises facing our human family call for far-sighted and united responses, I pray that your decisions will be guided by a concern for building a society marked by authentic justice and freedom," the pope said.

Kremlin spokesman Dmitry Peskov said Russia would seek "good relations with the United States", while a foreign ministry statement said they expected a "more constructive" approach to upcoming arms control talks.

The US and Russia are to discuss extending the landmark 2010 New START nuclear weapons accord shortly after Biden's swearing in.

Chancellor Angela Merkel said she was looking forward to a "new chapter of German-American friendship and cooperation".

"Warmest congratulations on your inauguration, @POTUS Joe Biden and @VP Kamala Harris -- a true celebration of American democracy," Merkel was quoted as saying in a tweet posted by her spokesman Steffen Seibert.

World leaders have congratulated Joe Biden on his inauguration as President of the United States
World leaders have congratulated Joe Biden on his inauguration as President of the United States AFP / MANDEL NGAN

French President Emmanuel Macron tweeted: "Best wishes on this most significant day for the American people!

"We are together. We will be stronger to face the challenges of our time. Stronger to build our future. Stronger to protect our planet. Welcome back to the Paris Agreement!," Macron wrote in English.

He was referring to the 2015 international accord committing all nations to cut carbon emissions to limit global warming, but which the United States under Trump formally quit in November last year.

Prime Minister Boris Johnson, who has faced criticism over his close relationship with Trump, said he was looking forward to "working closely" with Biden.

"In our fight against Covid and across climate change, defence, security and in promoting and defending democracy, our goals are the same and our nations will work hand in hand to achieve them," he said.

Queen Elizabeth II sent a private message to Biden before he was sworn in, Buckingham Palace said, without revealing the contents of the message.

"Today a true friend of Ireland @JoeBiden became the 46th President of the USA," Prime Minister Micheal Martin wrote on Twitter.

"It is a day of history and hope and I look forward to forging ever closer ties between our two great nations."

"Our two countries are more than neighbours -- we are close friends, partners, and allies," Prime Minister Justin Trudeau said, pledging Canada's cooperation in fighting the coronavirus pandemic, for climate action and for a sustainable economic recovery.

Indian Prime Minister Narendra Modi tweeted: "My warmest congratulations to @JoeBiden on his assumption of office as President of the United States of America. I look forward to working with him to strengthen India-US strategic partnership."

Japan's Prime Minister Yoshihide Suga tweeted his congratulations, adding "I look forward to working with you and your team to reinforce our alliance and to realize a Free and Open Indo-Pacific."

South Korean President Moon Jae-in hailed Biden's inauguration, saying: "America is back. America's new beginning will make democracy even greater. Together with the Korean people, I stand by your journey toward 'America United'."

The leaders of Kuwait, Qatar, Bahrain, Saudi Arabia and the United Arab Emirates all sent messages of congratulations.

Palestinian president Mahmud Abbas said he was "impatient" to work together with Biden "for peace and stability in the region and in the world".