BRUSSELS (Reuters) - Donald Trump’s fractious first meeting with NATO has left European allies wondering where the military alliance goes next, according to diplomats in Brussels who held a post-mortem on the U.S. president’s visit this week.

FILE PHOTO: NATO Secretary General Jens Stolenberg (L), U.S. President Donald Trump and Britain's Prime Minister Theresa May (R) attend a ceremony at the new NATO headquarters before the start of a summit in Brussels, Belgium, May 25, 2017. REUTERS/Christian Hartmann

After apparently moderating his stance toward an organization he once dismissed as obsolete, Trump used last week’s meeting to publicly denounce Europe’s low defense spending, while also surprising many NATO leaders present by urging them also to focus on illegal immigration.

Many at NATO headquarters are now unsure of the alliance’s future direction under Trump, according to seven current and former alliance diplomats, some of whom attended Tuesday’s debriefing at NATO’s inner sanctum, the North Atlantic Council.

“Trump showed we have fundamental differences about what NATO is for,” said one senior European NATO diplomat. “NATO is designed to defend the territory of its members, not stop terrorism or immigration. We are heading in opposite directions.”

A second diplomat described Trump’s style, which revealed the limits of negotiating in advance with U.S. diplomats and even with such senior figures as Defence Secretary James Mattis, as both “refreshing” because it was direct, but also as “very strange”.

The president’s criticism, the envoy said, carried risks for the United States by turning off Europe from NATO, sentiments already expressed by Germany and Norway.

At the dinner that followed Thursday’s summit, Merkel was visibly displeased by Trump’s NATO speech but did not challenge him, two diplomats present said. However, after a further couple of days with Trump at a G7 summit, she warned Europeans that the meetings had shown her they could not entirely count on “others” and must “take our fate into our own hands”.

A NATO official dismissed concerns about Europe losing U.S. protection, saying Thursday’s meeting had been a success. NATO Secretary-General Jens Stoltenberg told reporters immediately afterwards that Trump had sent “a strong signal” of support during his first visit to alliance HQ.

NOT AN “ACCEPTABLE BRAND”

Founded to deter the Soviet threat in 1949, the North Atlantic Treaty Organisation is based on deep cooperation with the United States, which provides for Europe’s security with its nuclear and conventional arsenals. NATO has found renewed purpose since Russia’s 2014 annexation of Crimea, sending battalions to the Baltics and Poland to deter any potential Russian incursions.

Under a decision taken by Trump’s predecessor Barack Obama, U.S. forces and weaponry are returning to eastern Europe in larger numbers than at any time since the end of the Cold War.

But Trump’s call for NATO to be on the front line against Islamic militants is more difficult for an alliance now wary of complex conflicts after more than a decade in Afghanistan.

Trump wants to see NATO taking a bigger role in the 68-member U.S.-led coalition against Islamic State. France and Germany have resisted, worried that the Western alliance’s presence may irk Arab members of the coalition and that NATO may be pushed into another open-ended foreign assignment.

“Not all allies accept that NATO is an acceptable brand in Iraq,” said Adam Thomson, a former British ambassador to NATO and now director of the European Leadership Network think-tank in London. “They are also worried about a slippery slope that leaves NATO holding the baby should the U.S. role diminish.”

In what some diplomats say is a sign of that risk, the United States is requesting more NATO troops from allies for Afghanistan, despite expectations of a gradual drawdown.

At the NATO meeting with Trump, the military alliance did agree to join the U.S.-led coalition against Islamic State. It will also set up a new intelligence unit to track foreign fighters and create a new post of counter-terrorism coordinator.

But Germany insists the decisions are mainly symbolic.

“The counter-terrorism measures are a fig leaf,” said Tomas Vasalek, a former Slovak ambassador to the alliance and now the director of the Carnegie Europe think-tank.

“The original sin was to form a coalition run by the U.S., not NATO, so NATO’s efforts are not going to be a game changer.”

SPEND! SPEND!

A senior U.S. official at the Brussels meeting said NATO could achieve Trump’s goals by increasing defense spending.

“The more NATO countries spend, the worse it is for Russia,” the official said. “What Trump’s doing really is increasing NATO’s ability to deter any kind of aggression on its borders.”

Many allies say Trump has a point about Europe’s drop in defense spending since the fall of the Soviet Union.

At a NATO summit in 2014, months after Russia’s annexation of Crimea, allies agreed to reach a target of spending 2 percent of economic output on defense every year by 2024.

Only the United States, Britain, Poland, Estonia and Greece met the target in 2016. Trump told leaders that “23 of the 28 member nations are still not paying what they should be paying.”

But Trump’s sharp words risk turning off some European allies from NATO, diplomats said.

Like many euro zone countries, indebted Italy, Spain and Belgium face European Union constraints on the budgets following years of financial crisis.