BRUSSELS >> President Donald Trump today chastised NATO leaders for not paying their fair share to protect the alliance, complaining in front of them that the defense burden the United States has shouldered for many years is “not fair” to its taxpayers.

Trump also did not explicitly affirm that an attack on any member of the 28-nation alliance is an attack on all.

Separately, Trump vowed to crack down on leaks that led British police to withhold information from the United States about the investigation into this week’s concert bombing.

Trump issued his sharp rebuke to NATO from Brussels — he once called it a hellhole — where he addressed leaders at both the European Union and NATO, alliances whose necessity he has questioned.

At a ceremony at NATO’s gleaming new headquarters, Trump reissued his longstanding call for members to pay their fair share, lecturing the expressionless leaders about spending more as they stood listening in awkward silence.

“This is not fair to the people and taxpayers of the United States,” Trump said in brief remarks, adding that many member nations owe “massive amounts of money from past years and not paying in those past years.”

“If NATO countries made their full and complete contributions, then NATO would be even stronger than it is today, especially from the threat of terrorism,” Trump said.

The 28 member nations, plus soon-to-join Montenegro, were to renew a previous commitment to move toward spending 2 percent of their gross domestic product on defense by 2024. Only five members currently meet the target: Britain, Estonia, debt-laden Greece, Poland and the United States, which spends more on defense than all the other allies combined.

Moreover, though the White House recently sent signals that the United States would stay in NATO’s mutual defense pact, known as Article 5, Trump made no mention of it as he stood next a monument dedicated to the only time the article has been invoked: during the terror attacks on September 11, 2001.

Asked about Trump not explicitly affirming U.S. support for Article 5, White House press secretary Sean Spicer said: “It goes without saying. His presence at this event underscores our commitments and treaty obligations.”

Trump’s speech to NATO came hours after the EU council president said a discussion with Trump produced sharply different views on Russia. In a separate meeting, France’s new president pushed Trump on a sweeping climate agreement and even engaged in an apparent handshake standoff.

Trump vowed a thorough review of leaks from his administration after a British official said today that Manchester police have decided not to share further information on the bombing investigation due to leaks blamed on U.S. officials. Trump, who said there is “no relationship we cherish more” than the one with the U.K., declared the leaks “deeply troubling” and said he was asking the Justice Department to lead an investigation into the matter.

“These leaks have been going on for a long time and my administration will get to the bottom of this,” Trump said in a written statement. “The leaks of sensitive information pose a grave threat to our national security.”

British Prime Minister Theresa May said she planned to discuss the leaks with her American counterpart at the NATO gathering to “make clear to President Trump that intelligence that is shared between our law enforcement agencies must remain secure.”

British officials are particularly angry that photos detailing evidence about the bomb were published in The New York Times, although it was unclear whether the paper obtained the photos from U.S. officials.

Trump, who unlike other leaders at the summit has no plans to formally address reporters, ignored shouted questions about whether the U.K. can trust the U.S. with sensitive material.

Trump and his aides have long complained about “leakers” they think are trying to undermine his presidency. While all administrations deal with some leaks, news outlets have been privy to everything from details of draft documents to the president’s private phone conversations with foreign leaders.

Recently in the news were reports that the president had shared highly classified information with Russian officials during an Oval Office meeting, revealed by those with knowledge of the conversation.

Trump’s remarkable public scolding of NATO came amid of backdrop of uncertainty in Brussels toward Trump over his past comments publicly cheering the United Kingdom’s vote last summer to leave the EU and slamming the alliance during his transition as “a vehicle for Germany.” Trump has taken a less combative tone since taking office, praising the alliance as “wonderful” and saying a strong Europe is very important to him and the United States.

After meeting with Trump today at the EU, European Council President Donald Tusk said he and the U.S. president agreed on the need to combat terrorism, but that some differences loomed large.

“Some issues remain open, like climate and trade. And I am not 100 percent sure that we can say today — we mean Mr. President and myself — that we have a common position, common opinions about Russia,” said Tusk, who said unity needed to be found around values like freedom and human rights and dignity.

Trump also had lunch with new French President Emmanuel Macron, who has been critical of the Republican president. As the press watched, the two men exchanged a very firm handshake during their meeting, both men gripping tight, their faces showing the strain.

Trump also scored a hoped-for win from NATO, which joined the 68-nation international coalition fighting the Islamic State group. An anti-terror coordinator may also be named. But most changes will be cosmetic, as NATO allies have no intention of going to war against IS.