US President Donald Trump has ignited a fresh diplomatic row with French President Emmanuel Macron, accusing him of "insulting" NATO.
Mr Trump, who is in London for a two-day summit of alliance leaders, said the French president had been "very disrespectful" after saying NATO was suffering "brain death".
Speaking during a breakfast meeting with NATO Secretary General Jens Stoltenberg at the US ambassador's residence, Mr Trump said: "I think that is very insulting to a lot of different forces.
"It is a very, very nasty statement.
"France is not doing well economically at all.
"It is a very tough statement to make when you have such difficulty in France.
"They have had a very rough year.
You just can't go around making statements like that about NATO. It is very disrespectful."
Mr Macron's comments followed Turkey's incursion against Kurds forces in north-east Syria after the withdrawal of US troops.
The Kurds played a key role in helping the West defeat so-called Islamic State (IS) in Syria.
Turkey did not inform NATO partners about its plans, leaving the allies alarmed by the move.
But Turkish President Recep Tayyip Erdogan has already defended his decision and dismissed Mr Macron's comments.
He accused the French president of having "a sick and shallow understanding" of terrorism, suggesting he was the one who was "brain dead".
Turkey's offensive has been widely criticised and has been accused of strengthening Russia and the Assad regime's grip on Syria.
Meanwhile, Turkey's decision to purchase Russian air defence systems has raised further alarm among the alliance.
Prime Minister Boris Johnson was due to host a meeting with Mr Macron, Mr Erdogan and German Chancellor Angela Merkel in Downing Street ahead of Wednesday's summit.
Downing Street said Mr Johnson would use the meeting to appeal for unity across the alliance.
"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," a Downing Street spokesperson 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."
That message was echoed by Defence Secretary Ben Wallace who said NATO's "comparative advantage" over its competitors had always hinged on its unity.
Speaking at a conference ahead of the summit he said the alliance "must stand together - no side deals, no separate voices".
Meanwhile, the NATO Secretary General dismissed Mr Macron's criticism.
"NATO is active, NATO is agile, NATO is adapting," Mr Stoltenberg said.
"We have just implemented the largest reinforcement of collective defence since the Cold War."
The formal NATO events will begin with a reception at Buckingham Palace hosted by the Queen on Tuesday evening.
The main talks will then take place on Wednesday at The Grove, a country house hotel near Watford.
The meeting is expected to consider new threats, including the areas of cyber and space.
Cover Image: US President Donald Trump at Winfield House (Picture: PA).