"America's back" was Joe Biden's message to the world as he became the first sitting U.S. president to address the annual Munich security conference, pledging to forge a strong transatlantic partnership with European leaders.

Welcoming the U.S.'s return to multilateralism after the four-year "Make America Great Again" era of Donald Trump, France's Prime Minister Emmanuel Macron also pledged to help Biden strengthen NATO and increase the financial contributions of its European members.

Macron told the virtual conference – the largest security gathering of its kind – France would finally meet its NATO pledge to spend 2 percent of its gross domestic product (GDP) on defense. The failure of European members of the 30-strong alliance to reach this target has long been a bugbear for U.S. leaders.

Speaking from Washington, Biden told his remote audience that "the partnership between the European Union and the U.S. must be the cornerstone of everything we must accomplish in the 21st century, just as it was in the 20th century."

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Repudiating his predecessor's isolationism and disdain for the intergovernmental military alliance, Biden said the U.S. was "fully committed to NATO." He added: "We'll keep faith with Article 5 in which an attack on one is an attack on all. That is our unshakeable vow."

Biden – who addressed the conference once in person as vice president and again after leaving office – said the U.S. was determined to re-engage with Europe and "earn your trust," a far cry from Donald Trump's unilateralism.

Both Macron and Germany's Chancellor Angela Merkel made thinly veiled attacks on Trump, with the former saying that Europe and the U.S. "need to act together in a coordinated way and respect all our allies, which has not always been the case." 

In her address, Merkel called the prospects for multilateralism vastly improved, adding "that has a lot to do with Joe Biden being the new president of the United States of America."

During his speech, delivered from Paris's Elysee Palace, Macron called on his fellow leaders to back internet regulation. He also urged fellow NATO members to work to improve relations with Russia, which have sunk to a post-Cold War low in recent years.

Biden, Macron and Merkel also called for renewed global cooperation on climate change. The U.S. president said he was "grateful for Europe's continued leadership on climate change in the last four years."

The trio backed the World Health Organization's ACT (Access to COVID-19 Tools) plan to distribute vaccines to poorer countries.

Earlier, World Health Organization Director-General Tedros Adhanom Ghebreyesus told the audience: "When people speak with one voice, governments listen. The longer it takes to suppress the virus everywhere, the more chance it will mutate and we could end up back at square one."

American business magnate and philanthropist Bill Gates, whose 2017 warning of the likelihood of a pandemic was largely ignored, said it was important for countries to start preparations for the next pandemic.

"Given the trillions of dollars of damages and deficits we have seen, we should make the investments to ensure that it won't happen again," he said.

The Munich conference has taken place every February since 1963 and usually lasts for several days. This year's online version lasted just a few hours.