U.S. President Donald Trump slammed NATO allies on Thursday for not spending enough on defense, and claimed that the allies owed the U.S. "massive amounts of money".
Speaking at a handover ceremony of the new NATO headquarters in Brussels, Trump sharply criticized member states for not meeting their financial obligations.
"23 of the 28 member nations are still not paying what they should be paying and what they are supposed to be paying for their defense. This is not fair to the people and taxpayers of the U.S." he said.
"And many of of these nations owe massive amounts of money from past years," he added without giving names.
U.S. media reported last month following a meeting between Trump and German Chancellor Angela Merkel that he gave her a $374 billion invoice for what Germany owed the U.S. for NATO defense.
NATO member states pledged in 2014 to stop defense cuts, and gradually increase their spending towards the aim of 2% of their GDP.
Trump argued that amid new security challenges, allies should further raise their contributions.
"Over the last eight years, the U.S. spent more on defense than all other NATO countries combined," he said.
"We should recognize that with these chronic underpayments and growing threats, even 2 percent of GDP is insufficient to close the gaps in modernizing, readiness and the size of forces. We have to make up for the many years lost," he added.
Leaders from 28 NATO member states gathered in Brussels on Thursday for a mini summit which focused on the fight against terrorism and fair burden-sharing among the allies.
It was the first NATO leaders' summit for Trump, British Prime Minister Theresa May and France’s new president, Emmanuel Macron.