Biden meets U.K. leader and King Charles before heading to NATO summit

London — President Biden was in London Monday morning for a whistlestop, 24-hour visit to the United Kingdom before heading later in the day for a NATO leaders summit in Lithuania. The first meeting on Mr. Biden's agenda after his Sunday night arrival was a sit-down with U.K. Prime Minister Rishi Sunak at his residence at No. 10 Downing Street. It was the president's first in-person discussion with a fellow world leader on the European trip as the U.S. and its NATO allies look to maintain a unified voice in support of Ukraine as it battles Russia's ongoing invasion.

Mr. Biden was heard saying as he walked into the British prime minister's official residence that the U.S. has "no closer friend and greater ally" and that the relationship remained "rock solid."  

There has been concern in Europe over the Biden administration's decision to send controversial weapons to Ukraine, but also over the future of U.S. government backing for Ukraine when Mr. Biden's first term comes to an end. On both points, the U.S. leader will be looking to reassure America's closest allies that Washington remains not only a committed partner but one that respects their humanitarian concerns.

Mr. Biden has spoken with Sunak a handful of times in recent months and their Monday meeting at Downing Street lasted only about 40 minutes. 

It came after the U.S. announced its latest military aid package for Ukraine, which for the first time includes controversial cluster munitions. The move has divided U.S. allies, some of which — including the U.K. — have banned use of the bombs under an international treaty signed in 2008 by some 123 nations.

A spokesman for Sunak's office said after he and Mr. Biden met that Britain stood "by our obligations under the convention, which include discouraging their use."

"There is no change from us on that," the spokesman told reporters, adding that "obviously, it is for each country to make a decision." 

The U.S., Russia and Ukraine are not signatories to the 2008 treaty. NATO Secretary General Jens Stoltenberg said Friday that NATO does not have a position on cluster munitions and that their use is not on the agenda for the summit that Mr. Biden will join in Lithuania after his stop in London.

After their meeting, the White House said Mr. Biden and Sunak had "reaffirmed their steadfast support for Ukraine in the face of Russia's ongoing aggression."

Another issue facing Mr. Biden, Sunak and then the other NATO leaders this week in Lithuania, is Sweden's pending accession to the transatlantic alliance. Russia's invasion of Ukraine drove the previously neutral countries of Finland and Sweden to apply for NATO membership. Finland has already become a full NATO member but Turkey and Hungary have so far blocked Sweden from joining.

Mr. Biden was expected to discuss with Sunak conditions for a possible deal with Turkey to clear the way, but the White House did not mention that topic in its read-out of their meeting.

Ukraine also wants to join NATO, but allowing that to happen would infuriate Russia, likely draw sharp criticism from China and is a more contentious issue among the alliance's existing members.

In an interview aired by CNN over the weekend, Mr. Biden said he didn't think Ukraine was "ready for membership in NATO."

"If the war is going on, then we're all in a war," he said, adding that there are other qualifications Ukraine must still meet to be considered for membership, including full "democratization."

After his meeting with Sunak, Mr. Biden left central London to head west for his first in-person meeting with King Charles III at Windsor Castle. Though not an official state visit, some classic British pomp and circumstance was organized for Mr. Biden's stop at the ancient home of the British monarchy, including a military Guard of Honor and a marching band.

Mr. Biden had met with Charles on multiple occasions, but not since the king's formal coronation ceremony on May 6. Mr. Biden did not attend the ceremony as he had just been in Britain for a separate trip, but first lady Jill Biden was there. 

The U.S. president spent about two hours at Windsor on Monday, but his meeting with the king was private.  

The two heads of state met at the COP26 climate summit in Scotland, in November 2021, and on Monday, they discussed environmental issues and greeted attendees from a climate finance forum that took place in the morning. Mr. Biden and Charles met business leaders and had been expected to discuss how private industry can best seek to tackle climate change.

Haley Ott is an international reporter for CBS News based in London.