US President Joe Biden has arrived in Britain on the first leg of his five-day tour of Europe, during which he will attend a NATO summit.

Biden flew to Britain on Air Force One after leaving a military base in the eastern US state of Delaware on Sunday.

He will meet British Prime Minister Rishi Sunak and King Charles on Monday. Biden will then travel to the Baltic country of Lithuania to take part in a NATO summit scheduled to open on Tuesday.

The summit is expected to focus on aid for Ukraine in its fight against Russia. Biden will likely use the meeting to confirm leaders' commitment to continue supporting Ukraine. He will also likely try to lead discussions on strengthening defense in the long term.

Prior to the trip, Biden commented on Ukraine's ambition to join NATO in an interview aired by CNN on Sunday.

The president said it is going to "take a while" for Kyiv to meet all qualifications for NATO membership. He added that while the process is underway, the US is "ready" to provide Ukraine with weaponry and "the capacity to defend" itself.

Biden is expected to back Sweden's bid for NATO membership. After the summit, he plans to meet Nordic leaders in Finland, which acceded to the alliance in April.