BRUSSELS — In a statement issued amid meetings with foreign leaders, Trump responded to British outrage over the leaks by calling them “deeply troubling” and vowing to “get to the bottom of this.”

He added: “The leaks of sensitive information pose a grave threat to our national security. I am asking the Department of Justice and other relevant agencies to launch a complete review of this matter, and if appropriate, the culprit should be prosecuted to the fullest extent of the law. There is no relationship we cherish more than the Special Relationship between the United States and the United Kingdom.”

Trump was expected to get an earful Thursday from British Prime Minister Theresa May, following the apparent leak of shared intelligence information from Monday’s Manchester bombing that appeared in the U.S. media. May said after a Thursday cabinet meeting that she would “make clear” to Trump “that intelligence that is shared between our law enforcement agencies must remain secure.”

When reporters asked Trump, as he sat for cameras with Macron before their lunch, whether he wanted to say anything about British intelligence sharing, Trump said only, “Thank you.” Asked if his fired national security adviser, Michael Flynn, should cooperate with FBI and congressional investigations on collusion with Russia, Trump stared at the source of the question and again said, “Thank you,” as the press was hustled out of the room.

Trump is already under fire at home for violating intelligence agreements, following a Washington Post report that he revealed sensitive information on the Islamic State, obtained from Israel, to the Russian foreign minister and ambassador.

Earlier Thursday, the European Union’s top political leader said after a meeting with Trump that the West needs to concentrate on “values . . . not just interests.”

“Values and principles first, this is what we – Europe and America – should be saying,” Donald Tusk, president of the European Council, told reporters after spending a half-hour with Trump. Tusk, who has expressed concern before about the new U.S. administration, said he and Trump agreed on counterterrorism but did not see eye to eye on a number of issues, including climate, trade and Russia.

The EU meeting, with Tusk and European Commission President Jean-Claude Juncker, provided Trump with a taste of what he is likely to hear later Thursday when he holds his first formal meeting with his NATO counterparts – and at least some of what they can expect to hear from him.

NATO leaders will hold a working dinner Thursday night. After the EU meeting, Trump had a private lunch with new French President Emmanuel Macron at the residence of the U.S. ambassador to Belgium, where Trump is staying in Brussels. Trump greeted Macron at the door with a handshake and a hearty “How are you?” as Macron stepped out of his black limousine. France has urged Trump not to pull out of the 2015 Paris climate accord, a decision he has hinted at but that the administration says has not yet been made.

On this fourth and penultimate stop on Trump’s nine-day trip, the first overseas travel of his presidency, Trump is unlikely to find the near adulation he experienced from Arab leaders in Saudi Arabia, and from the Israeli government in Jerusalem. At those stops, they agreed with Trump’s call to concentrate on counterterrorism and economic growth, with no discussion, at least in public, about human and civil rights concerns that had dogged U.S.-Middle East relationships under President Barack Obama.

Beyond its official purpose of opening the alliance’s new $1.2 billion headquarters here, the NATO meeting was scheduled to allow Trump and leaders of NATO states to take the measure of each other. In addition to talking about values, climate change, trade and Russia, the 27 other members hope to relieve anxiety that arose during Trump’s campaign, when he questioned why the United States was spending its own money to defend Europe, called NATO “obsolete” and ill-equipped to deal with terrorism, and threatened to withdraw if other members failed to pay their “fair share.”

Administration officials such as Defense Secretary Jim Mattis and Secretary of State Rex Tillerson have publicly tempered some of those views since Trump’s inauguration. Mattis has said that the United States commitment to NATO members’ pledge to defend each other, under Article 5 of the alliance’s charter, is “rock solid.”

Some allies feel that the golden word of the president would finalize the message to Russia and others across the NATO borders.

“That would be important if the president personally and explicitly states it,” said Latvian Foreign Ministry State Secretary Andrejs Pildegovics, who was in Brussels for the meeting. “At the end of the day, all important decisions are made by the president. And usually the president has a few options on the table.”

While Trump is still expected to call for alliance members to speed the increases in their defense budgets, he has acknowledged progress in bringing their domestic defense spending up to 2 percent of their budgets by 2024.

NATO Secretary General Jens Stoltenberg also said Thursday morning that the alliance was ready to join the U.S.-led coalition against the Islamic State, although he said NATO would not have a combat role on the ground in Iraq and Syria. Among increased contributions to counterterrorism, he said the alliance would step up support of NATO AWACS aircraft and intelligence-sharing, and would provide refueling capabilities.

“We will now establish a new intelligence fusion cell at the headquarters addressing terrorism, including foreign fights. And we will also appoint a special coordinator for NATO’s efforts fighting terrorism,” Stoltenberg said. He called it a “strong political message,” as well as a practical one.

Stoltenberg also said NATO would consider increasing its noncombat troop presence in Afghanistan. The Trump administration is currently reviewing the U.S. presence there, including adding up to 5,000 troops to the nearly 10,000 already there and expanding their role assisting Afghan government forces fighting both the Taliban and a local Islamic State presence.

Tillerson told reporters Wednesday that “we have not completed the Afghan policy review,” adding: “It’s probably a couple of weeks away at least before we’re going to be ready to present something to the president.”

In a brief midday news conference, Stoltenberg said the alliance has already “turned a corner” on spending and that budgets have increased for the last two years. All members, he said, have “started to move toward spending 2 percent. Picture still mixed, but it is much better than was two years ago,” and NATO expects to adopt a plan that would further speed the increases.

The “reality,” Stoltenberg said, is that decreased tensions following the end of the Cold War resulted in reduced spending. “Now we see tensions are going up, and we have to invest more in our shared security.”

Trump’s packed schedule in a city he once called a “hellhole” took him from one meeting to another with partners and allies who wondered which president would show up: the disciplined script-bound leader who has made mostly conventional public remarks during his international trip, or the one who has kept them in the crosshairs.

Tusk, in his comments after meeting Trump, hinted at a mild clash at least. “My main message to President Trump,” he said, “was that what gives our cooperation and friendship its deepest meaning are fundamental Western values, like freedom, human rights, respect for human dignity. The greatest task today is the consolidation of the whole free world around those values, not just interests.”

EU and NATO leaders have done their best to ease Trump’s trip. Several thousand protesters on Thursday were kept miles away from Trump’s arrival meeting with the Belgian king, limiting the chance he would see dissenters out the window of his armored limousine as he sped through town. Much of the Brussels center was shut down under security that was heavy even for a city that routinely holds 28-leader summits of the European Union.

NATO’s leaders used the excuse of the vast new headquarters to invite the former real estate mogul for a ribbon-cutting, even though construction on the site – a former military airfield – is not yet finished.

As part of the official headquarters opening, Trump will dedicate a memorial to the World Trade Center – formed with a piece of the fallen towers. German Chancellor Angela Merkel will do the same for a separate memorial containing a peace of the Berlin Wall.