NATO kicked off tense summit talks on Wednesday seeking to make a show of unity despite bickering among leaders as a festering row with Turkey rumbles on. What should have been a celebration of NATO's 70th birthday has been overshadowed by bitter disputes 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 defense spending, but 2019's provocateur was 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 defense 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 Daesh (the so-called IS) in Syria as "terrorists". NATO Secretary General Jens Stoltenberg opened the sole summit working session hailing increased European and Canadian defense spending — a key Trump demand. But barely two hours before the meeting 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 of the revised defense 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." Diplomatic sources said the leaders of the three Baltic countries and Poland would meet Erdogan for talks on the issue, while 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. The leaders met in various groups in London on Tuesday before attending a reception 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 gossiping about Trump's lengthy media appearances. After Macron's one-on-one pre-summit meeting with Trump had been preceded by a long 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." 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 defense 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, saying as he arrived at the summit that he was glad to have moved the NATO conversation on from money to matters of strategy. On Tuesday he turned his fire on Turkey, noting that its forces have attacked the Kurdish militia that backed the allies against Daesh in Syria. And he accused Ankara of working with "ISIS (Daesh) proxies". Macron and Erdogan later came face to face at four-way talks with German Chancellor Angela Merkel and Britain's Johnson. Trump defended Stoltenberg's record of pushing allies for increased defense 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 defense 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 defense before 2024. Trump, who cited in particular Germany as falling short for spending only 1.2 percent of GDP, was scheduled to hold lunch talks with the so-called "two percenters".