US President Donald Trump (3rd from left) speaks during a working lunch at the NATO summit at the Grove hotel in Watford, London, on 4 December 2019. (AFP)

NATO (North Atlantic Treaty Organization) leaders vowed to stick together against threats from Russia and terrorism and recognized the challenge of a rising China on Wednesday, despite another summit overshadowed by US President Donald Trump’s angry outbursts.

The 29 leaders meeting outside London to mark the 70th anniversary of the Atlantic alliance agreed a joint statement despite divides over spending and strategy and sharp exchanges between several of the heads of state.

But the bad blood continued to the end of the two-day get together, with Trump branding Canada’s Prime Minister Justin Trudeau “two-faced” after a group of allied leaders were caught on video at a Buckingham Palace reception mocking the US leaders’ rambling press appearances.

Trump cancelled his planned final news conference to fly directly back to Washington, despite boasting of having convinced his European allies to boost defense spending and Turkey to drop its objections to the adoption of an updated defense plan for the Baltic states and Poland.

The second and final day of the get together began with the release of a video showing Trudeau, France’s President Emmanuel Macron, Britain’s Prime Minister Boris Johnson and the Netherlands’ Mark Rutte joking together about how Trump had delayed the previous days meetings.

Trump was furious, and criticized the Canadian leader for not meeting NATO members’ target of spending two percent of their GDP on defense.

“Well, he’s two-faced,” he said. “And with Trudeau, he’s a nice guy. I find him to be a nice guy, but the truth is, I called him out on the fact that he’s not paying two percent, and I guess he’s not very happy about it.”

The run-up to the summit had been marked by Macron branding the alliance “brain dead” and demanding a new strategy, reopening a dialogue with Russia and refocusing on the fight against Islamist terrorism.

Turkey’s President Recep Tayyip Erdogan, meanwhile, had threatened to block the updated Baltic defense plan unless his allies agreed to brand the Kurdish militias of northeastern Syria who helped defeat the Islamic State group “terrorists”.

But despite the rancor, the 29 managed to agree a “London Declaration” and Turkey withdrew its objections after Trump held an unscheduled side meeting with Erdogan.

“In challenging times, we are stronger as an alliance, and our people safer,” the declaration said.

“Our bond and mutual commitment have guaranteed our freedoms, our values, and our security for 70 years.”

The statement was the first from NATO to acknowledge the growing strategic challenge posed by China, and also stressed the need for a stronger coordinated response against terrorism.

It held out the possibility of “a constructive relationship with Russia when Russia’s actions make that possible” but stressed the threat posed by Moscow’s deployment of intermediate range nuclear missiles.

And, in a nod to French and German concerns about NATO’s strategic direction, the members asked Secretary General Jens Stoltenberg to consult experts to strengthen the alliance’s “political dimension.”

Leaders of NATO alliance countries join Queen Elizabeth II and the Prince of Wales at the Buckingham Palace. (AFP)

On Tuesday, the leaders met in various groups in London 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.

In recent weeks Macron 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 but the French leader stood by his approach, saying that he was glad to have moved the NATO conversation on from money to matters of strategy.

Macron also turned his fire on Turkey, noting that its 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”.

Trump has defended Stoltenberg’s record of pushing allies for increased defense spending, but he reiterated his own long-standing complaints.

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, who cited in particular Germany as falling short for spending only 1.2 percent of GDP, held lunch talks with the so-called “two percenters.”