NATO leaders sought to make a show of unity on Wednesday as they met to conclude their annual summit, but the alliance's chief admitted a festering row with Turkey was still unresolved.
What should have been a celebration of NATO's 70th birthday has been overshadowed by bitter rows about money and the future strategy of the alliance.
Last year, the Western allies' get-together was derailed by US President Donald Trump's demand for greater European defence spending, but 2019's provocateur was France's Emmanuel Macron.
The French president has called for a renewed strategic dialogue with Moscow and demanded that Turkey explain itself over its assault -- backed by Syrian rebels Paris sees as extremists -- on Kurdish forces and its purchase of the Russian S-400 air defence system.
Turkish President Recep Tayyip Erdogan meanwhile has threatened to hold up NATO efforts to bolster the protection of the Baltic republics against Russia unless the allies brand the Kurdish militias who defeated the IS group in Syria as "terrorists".
Amid fears Erdogan could even veto the summit declaration and with barely two hours to go before the leaders sat down for their sole roundtable, NATO Secretary General Jens Stoltenberg admitted a solution to the row with Turkey had still not been found.
"I'm confident that we will be able to find a solution to the issue related to the updating the revised defence plans," he said as he arrived for the summit at a luxury golf hotel in Watford, on the outskirts of London.
"I discussed this with President Erdogan last night and we are working on the issue as we speak."
The summit host, British Prime Minister Boris Johnson, played down the dispute.
"There is far, far more that unites us than divides us, and I think one thing every leader here is absolutely resolved upon is the vital importance of NATO for our collective security," he said as he arrived.
The leaders met in various groups in London on Tuesday before having dinner with Queen Elizabeth II in Buckingham Palace, but Macron refused to withdraw his charge that NATO strategy is "brain dead" and Trump continued to insist some capitals were "delinquent" in paying their way.
The row set up a tense last day of what NATO had hoped would be a 70th anniversary show of unity for the "most successful military alliance in history", and a demonstration that the West can stand up to challenges from Russia and China.
Adding to the disjointed mood, the leaders of Britain, Canada, France and the Netherlands were caught on camera at the palace reception mocking Trump's lengthy media appearances.
After Macron's one-on-one pre-summit meeting with Trump had been preceded by a lengthy question and answer session with the media, Johnson was seen asking him: "Is that why you were late?"
Canada's Prime Minister Justin Trudeau interjects: "He was late because he takes a 40 minute press conference off the top."
The leaders are to hold just one three-hour working session followed by a statement, and Johnson will make an appeal for unity.
In recent weeks Macron has tried to shake up the agenda by demanding a review of alliance strategy, but Trump -- who arrived boasting that he had forced members to boost defence spending -- hit back hard.
"I think that's very insulting," Trump said of Macron's assertion last month that NATO is experiencing "brain death".
"Nobody needs NATO more than France," he warned. "It's a very dangerous statement for them to make."
Trump later softened his tone at a joint appearance with Macron, but the French leader stood by his approach -- and his choice of language -- and turned his guns on Turkey.
He noted that Turkish forces have attacked the Kurdish militia that backed the allies against the Islamic State in Syria, and he accused Ankara of working with "ISIS proxies".
Macron and Erdogan later came face to face at four-way talks with Merkel and Britain's Johnson.
Merkel said she was "relatively optimistic" after the meeting, but Macron warned that "not all clarifications were obtained and not all ambiguities were resolved".
Trump defended Stoltenberg's record of pushing allies for increased defence spending, but he reiterated his own long-standing complaints.
"When I came in, I was angry at NATO, and now I've raised $130 billion," Trump said, referring to the sum Stoltenberg says Canada and European members since 2016 will have added to defence budgets by next year.
Only nine of NATO's 29 members have reached the target agreed at its 2014 summit to spend two percent of their GDP on defence before 2024.
Trump cited in particular Germany as falling short, spending only 1.2 percent of GDP.
Copyright AFP. All rights reserved.