Mr Trump told attendees at the Nato summit in Brussels this week that every member nation should be spending 4 per cent of their GDP on defence annually.
“President Trump wants to see our allies share more of the burden and at a very minimum meet their already stated obligations,” White House press secretary Sarah Huckabee Sanders said in a statement.
Mr Trump falsely claimed earlier this week that the US already spends 4 per cent of its GDP on defence. According to Nato, the US spent 3.57 per cent of its GDP on defence last year, and is projected to spend 3.5 per cent this year.
Mr Trump has long complained that other 28 Nato member countries do not contribute enough money towards their own defence, claiming the US is footing the bill for their protection. He previously raised the issue of increased spending targets with Nato Secretary General Jens Stoltenberg when he visited the White House last year.
Mr Stoltenberg said on Wednesday that the member countries were working towards a goal of spending 2 per cent of their respective GDPs on defence – a number agreed upon at a 2014 summit in Wales.
The announcement appeared not to impress Mr Trump, who tweeted: "Why are there only 5 out of 29 countries that have met their commitment? The US is paying for Europe’s protection, then loses billions on Trade. Must pay 2% of GDP IMMEDIATELY, not by 2025.”
Mr Trump reportedly sent letters to several Nato member countries ahead of the summit, accusing them of underspending on their defence and warning that the current situation was “no longer sustainable” for the US.
The summit itself has started on a tense note, with Mr Trump tearing into Germany during a breakfast meeting. The president accused Germany of skimping on its defence payments while giving “billions and billions of dollars a year to Russia” – a situation he called “very inappropriate”.
German Chancellor Angela Merkel shot back, noting that Germany is the the second largest donor of troops to the alliance, and remains “strongly committed” to supporting the US in Afghanistan.
She also responded to Mr Trump’s claim that Germany was a “captive” of Russia, saying: “I wanted to say that, because of current events, I have witnessed this myself, that a part of Germany was controlled by the Soviet Union. And I am very happy that we are today unified in freedom as the Federal Republic of Germany.”