WASHINGTON, June 29 (Xinhua) -- U.S. President Donald Trump reiterated his dissatisfaction on Friday with Germany and other European countries on their defense spending ahead of his Europe trip to attend a NATO summit.

"Germany has to spend more money," Trump told reporters on Air Force One en route to New Jersey.

Trump also singled out Spain and France for their failure to reach the two-percent-of-GDP benchmark for their defense budgets, claiming that "it's not fair what they've done to the United States."

NATO members will convene on July 11-12 in the Belgian capital Brussels, with military spending expected to top the agenda.

"NATO is very interesting, we'll see what happens there," said Trump, who is expected to attend the summit, followed by his meeting with Russian President Vladimir Putin.

Trump has long been scolding NATO nations for not fulfilling their commitment on defense spending.

It's been estimated that eight NATO allies will reach the two-percent benchmark by the end of this year, and 15 are on track to spend two percent by 2024.

German Defense Minister predicted in May that the German military budget would only grow gradually from currently 1.24 percent of GDP to 1.3 percent in 2019 and 1.5 percent in 2025.

France is near the two-percent target, with 1.8 percent in 2017, while Spain was at 0.92 percent last year.