BRUSSELS — President Donald Trump on Thursday reaffirmed his commitment to the NATO alliance after he said member nations caved to his demands by making significant pledges to increasing defense spending.

“The United States’ commitment to NATO remains very strong,” Trump told reporters at a surprise news conference following an emergency session of NATO members held to address his complaints.

Trump has berated members of the alliance for failing to spend enough of their money on defense, accusing Europe of freeloading off the U.S. and raising doubts about whether he would come to members’ defense if they were attacked.

Trump said he made his anger clear to allies on Wednesday.

“Yesterday I let them know that I was extremely unhappy with what was happening,” Trump said, adding that, in response, European countries agreed to up their spending.

“They are going to up it to levels like they have never though it before,” he said. He did not specify which countries had committed to what NATO countries in 2014 committed to spending 2 percent of their gross domestic products on defense by 2024, but NATO has estimated that only 15 members, or just over half, will meet the benchmark by 2024 based on current trends.

Earlier Thursday, Trump called out U.S. allies on Twitter as he attended a second day of meetings with leaders of the military alliance.

In a series of tweets from Brussels, Trump said “Presidents have been trying unsuccessfully for years to get Germany and other rich NATO Nations to pay more toward their protection from Russia.”

He complained the United States “pays tens of Billions of Dollars too much to subsidize Europe” and demanded that member nations meet their pledge to spend 2 percent of GDP on defense, which “must ultimately go to 4%!”

Trump has taken an aggressive tone during the NATO summit, questioning the value of an alliance that has defined decades of American foreign policy, torching an ally and proposing a massive increase in European defense spending.

Under fire for his warm embrace of Russia’s Vladimir Putin, Trump on Wednesday turned a harsh spotlight on Germany’s own ties to Russia, alleging that a natural gas pipeline venture with Moscow has left Angela Merkel’s government “totally controlled” and “captive” to Russia.

He continued the attack Thursday, complaining that “Germany just started paying Russia, the country they want protection from, Billions of Dollars for their Energy needs coming out of a new pipeline from Russia.”