Joe Biden arrived in Britain on Wednesday in his first foreign trip as US president, during which he is to visit several European countries.
The president arrived at the Royal Air Force Mildenhall base in eastern England in the evening together with First Lady Jill Biden.
"We are going to make it clear that the United States is back and democracies of the world are standing together to tackle the toughest challenges and the issues that matter most to our future," Biden said in front of US soldiers at Mildenhall, according to Britain's Press Association (PA).
"To tackle this century's most pressing challenges we have to do it together, we have to end Covid-19, not just at home but everywhere," Biden said.
He also called for "co-ordinated multilateral action" to tackle climate change.
On Thursday, Biden is due to meet British Prime Minister Boris Johnson near Cornwall, where the G7 summit takes place from Friday to Sunday, on the fringes of which Biden is expected to meet German Chancellor Angela Merkel, among other G7 leaders.
At the end of their visit to Britain, the US president and the first lady are to be received by Queen Elizabeth II at Windsor Castle near London on Sunday.
NATO summit, Putin
On Monday, Biden plans to attend the NATO summit in Brussels, where a top-level meeting with EU representatives is scheduled for the following day.
On Wednesday of next week, Biden is expected to hold an eagerly awaited summit with Russian President Vladimir Putin in Geneva before the US president returns to Washington.
"We're not seeking conflict with Russia. We want a stable, predictable, predictable relationship," Biden said on Wednesday evening.
"But I've been clear, the United States will respond in a robust and meaningful way when the Russian government engages in harmful activities," he added.
Earlier, the White House said: "This trip will highlight America's commitment to rallying the world's democracies, coming together to shape the rules of the road for the 21st century, defend our values, and tackle the world's biggest challenges."