Paris — European nations and Canada pushed back against accusations they don’t spend enough on defense after receiving a scolding from U.S. President Donald Trump.

Trump, who travels to Brussels next week to attend a potentially testy North Atlantic Treaty Organization summit, sent letters to several allied nations calling on them to increase their military budgets.

“It will become increasingly difficult to justify to American citizens why some countries continue to fail to meet our shared collective security commitments,” Trump said in a letter addressed to Norwegian Prime Minister Erna Solberg.

Norway, he wrote, “remains the only NATO ally sharing a border with Russia that lacks a credible plan to spend 2 percent of its gross domestic product on defense.”

Italy, Germany, the Netherlands, Canada and Spain also confirmed receiving a version of the letter. The New York Times, in a report on Tuesday, said it was sent to Belgium, Luxembourg and Portugal too. One NATO country government official, speaking on condition of anonymity ahead of the July 11-12 summit, said they understood that all members of the bloc received a letter.

At a NATO leaders’ meeting in May 2017, Trump refused to offer an explicit endorsement of the alliance’s collective-defense clause and instead hectored fellow leaders to meet the 2 percent target. Concern is running high in many European capitals over the outcome of this year’s summit after Trump last month revoked his endorsement of a Group of Seven communique praising free trade, insulted Canadian Prime Minister Justin Trudeau and then scheduled a July 16 meeting in Helsinki with Russian President Vladimir Putin.

Trump, though, is committed to the NATO alliance, said a White House official, who spoke on condition of anonymity.

Norwegian Defense Minister Frank Bakke Jensen said in a statement confirming receipt of the letter that Norway has increased defense spending 24 percent in real terms since 2013, and that spending on equipment is 27 percent of its budget, above the NATO average. Norway has recently taken delivery of Lockheed Martin F-35 fighters and Boeing P-8 surveillance aircraft.

“Burden sharing will be a key issue at the NATO Summit in July, and Norway looks forward to continued discussions on this issue,” Jensen said.

NATO said last month its European members and Canada would increase defense spending for a fourth year in 2018. Spending will rise 3.8 percent, bringing cumulative growth since the start of 2015 to about 15 percent or $87.3 billion.

In 2014, NATO members pledged to spend at least 2 percent of economic output on defense by 2024. In Europe, only Estonia, Greece and the U.K. achieved the goal last year. Poland, one of Europe’s fastest-growing economies, was at 1.99 percent. The U.S. led with expenditure of 3.6 percent of GDP, while Canada was at 1.3 percent.