UK Prime Minister Boris Johnson is set to call for North Atlantic Treaty Organisation- (Nato) unity amid growing tensions within the military bloc.
A summit to mark the founding of the 29-member defence alliance 70 years ago gets under way near London on Tuesday.
The gathering is overshadowed by a bitter row between France and Turkey, and a continuing debate over money.
Last month, French President Emmanuel Macron described Nato as “brain dead”, saying alliance members were no longer co-operating on a range of key issues.
US President Donald Trump, who has repeatedly clashed with Nato’s European members over the funding of the bloc, is among world leaders attending.
He arrived in the UK on Monday ahead of a reception to be hosted by the Queen at Buckingham Palace on Tuesday evening. Mr Trump is set to hold separate talks with the German and French leaders, and Nato’s secretary-general.
Nato members pledge to come to the aid of one another should any of the allies come under attack.
As host of the two-day summit, Mr Johnson is expected to reiterate the importance of Nato staying united.
“The PM’s position is that Nato is the most enduring and successful alliance in military history and that it continues to adapt to the evolving threats that we face,” the prime minister’s spokesman said.
“It is the cornerstone of Euro-Atlantic security and it helps to keep a billion people safe.
“The PM will emphasise that all members must be united behind shared priorities so Nato can adapt to the challenges ahead,” the spokesman added.
Tensions have grown since the election of President Trump, who has repeatedly complained that Europe’s Nato members are not contributing enough to the alliance.
Ahead of his visit, he tweeted to take credit for a recent commitment by Nato Secretary-General Jens Stoltenberg to increase spending levels.
Nato estimates for 2019 show there are now eight countries – in addition to the US –meeting the target agreed by all Nato members to spend 2% or more of their gross domestic product (GDP, a measure of economic output) on defence.
Mr Stoltenberg said on Friday that by 2020, European allies and Canada would have invested $130bn more since 2016 – the year President Trump was elected.
Nato is the world’s most powerful regional defence alliance which was set up in 1949 after the second world war amid anxiety at Soviet expansion.
It was founded on the principle of collective defence between allies.Nato originally had 12 founding members, but now has 29.