European leaders have voiced relief at Joe Biden’s inauguration, hailing a “new dawn” for Europe and the US, but warned that the world has changed after four years of Donald Trump’s presidency and that transatlantic ties will be different in future. “This new dawn in America is the moment we’ve been awaiting for so long,” Ursula von der Leyen, the European commission president, told MEPs. “Once again, after four long years, Europe has a friend in the White House.” The head of the EU’s executive arm said Biden’s swearing-in was “a demonstration of the resilience of American democracy”, and that the bloc stood “ready to reconnect with an old and trusted partner to breathe new life into our cherished alliance”. But Von der Leyen said relief should not lead to illusion, since while “Trump may soon be consigned to history, his followers remain”. A study this week showed that while many Europeans welcomed Biden’s election victory, more people than not felt that after four years of Trump the US could not be trusted, and a majority believed Biden would not be able to mend a “broken” country or reverse its decline on the world stage. The EU has invited Biden to a summit and top-level Nato meeting when he is ready, with Charles Michel, the president of the European council, calling for “a new founding pact” to boost multilateral cooperation, combat Covid, tackle climate change and aid economic recovery. Britain’s prime minister, Boris Johnson, who has faced criticism for his close relationship with Trump, said he was looking forward to working closely with Biden, citing a host of policy areas in which he hoped to collaborate. “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,” Johnson said in a statement. The German president, Frank-Walter Steinmeier, said he was “greatly relieved” at Biden’s inauguration, hailing “a good day for democracy”. He said democracy under the Trump administration had faced “tremendous challenges and endured … and proved strong”. Steinmeier said the transfer of power to Biden brought with it “the hope that the international community can work together more closely”, and he said Germany was looking forward “to knowing we once more have the US at our side as an indispensable partner”. However, he said that “despite the joy of this day”, the last four years had shown that “we must resolutely stand up to polarisation, protect and strengthen our democracies, and make policy on the basis of reason and facts”. Italy’s prime minister, Giuseppe Conte, said his country was “looking forward to the Biden presidency, with which we will start working immediately.” He said the two countries had a strong common agenda, including “effective multilateralism, climate change, green and digital transition and social inclusion”. The Spanish prime minister, Pedro Sánchez, said Biden’s victory represented “the victory of democracy over the ultra-right and its three methods – massive deception, national division, and abuse, sometimes violent, of democratic institutions.” Five years ago, Sánchez said, the world had believed Trump to be “a bad joke. But five years later we realised he jeopardised nothing less than the world’s most powerful democracy.” The Portuguese prime minister, António Costa, whose country holds the EU’s rotating presidency, said it was ready to work with Biden “from day one, to strengthen EU-US relations, reaffirm the enduring relevance of Nato and reinforce multilateral responses to climate change, defence of democracy and human rights”. In a notable reaction from beyond electoral politics, the climate activist Greta Thunberg tweeted a photo of Trump – whose decision to take the US out of the Paris climate accord Biden will reverse – outside the helicopter in which he left the White House. “He seems like a very happy old man looking forward to a bright and wonderful future. So nice to see!” Thunberg said, a reference to a condescending comment he tweeted about her after her speech to the UN climate forum in 2019. The Pope said he was praying that Biden’s decisions would “be guided by a concern for building a society marked by authentic justice and freedom”, and that God would guide the efforts of the new president – who is a Catholic – “to foster understanding, reconciliation and peace within the US and among the nations of the world”. In Russia, the former Soviet leader Mikhail Gorbachev called on Moscow and Washington to repair their ties. “The current condition of relations is of great concern,” he said. “But this also means that something has to be done about it in order to normalise relations. We cannot fence ourselves off from each other.” Among the US’s more outspoken foes, Iran, which has repeatedly called on Washington to lift sanctions imposed over its nuclear drive, did not miss the chance to celebrate Trump’s departure. “A tyrant’s era came to an end and today is the final day of his ominous reign,” said the president, Hassan Rouhani. “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.” Biden’s administration has said it wants the US back in the landmark Iran nuclear accord from which Trump withdrew, providing Tehran returns to strict compliance. The Nato chief, Jens Stoltenberg, said the military alliance hoped to strengthen transatlantic ties under the new president, adding that the world faced “global challenges that none of us can tackle alone”.