Donald Trump has been vocal about the defence spending of NATO members on a number of occasions (Picture: PA).
A former Danish prime minister has hit back at Donald Trump for comments the US President made about Denmark's defence spending.
Mr Trump criticised Denmark for "only" spending 1.35% of its GDP on defence.
NATO guidelines state member nations should contribute 2% of GDP on defence.
"They are a wealthy country and should be at 2%," the US President tweeted.
"We protect Europe and yet, only 8 of the 28 NATO countries are at the 2% mark.
"The United States is at a much, much higher level than that."
Mr Trump's comments came after he cancelled a visit to Denmark, describing the country's leader Mette Frederiksen as "nasty" after she rejected his idea of buying Greenland.
For the record, Denmark is only at 1.35% of GDP for NATO spending. They are a wealthy country and should be at 2%. We protect Europe and yet, only 8 of the 28 NATO countries are at the 2% mark. The United States is at a much, much higher level than that....— Donald J. Trump (@realDonaldTrump) August 21, 2019
Former Danish prime minister, Lars Loekke Rasmussen, responded by saying their commitment to defence is not just about the amount of money spent.
Mr Loekke Rasmussen, who led the country until June, tweeted the US President saying "We have had (proportionally) exactly the same numbers of casualties in Afghanistan as US."
He continued: "We will not accept that our defence willingness is only about percentages."
And - as i told You at the NATO Summit in Bruxelles last year - we have had (proportionally) exactly the same numbers of casualties in Afghanistan as US. We always stands firm and ready - so we will not accept that our defence willingness is only about percentages.— Lars Løkke Rasmussen (@larsloekke) August 21, 2019
Mr Trump has been vocal about wanting more NATO members to meet the alliance's 2% defence spending guideline.
Earlier this year, he was thanked by NATO Secretary-General Jens Stoltenberg for his "strong leadership" on the issue.
During his tweets about Denmark on Wednesday, Mr Trump said: "Because of me, these countries have agreed to pay ONE HUNDRED BILLION DOLLARS more - but still way short of what they should pay for the incredible military protection provided."
In January, a coalition in the Danish parliament agreed to add 1.5 billion kroner (£180 million) to the already agreed defence budget for 2023, which would put spending at 1.5% of gross domestic product for that year.
The US spends about 3.4% of its GDP on defence.
On Tuesday, Mr Trump cancelled his planned September visit to Denmark after Ms Frederiksen called his idea to buy Greenland "an absurd discussion".
He said her comment was "nasty" and "an inappropriate statement".
"All she had to say was say, 'No, we wouldn't be interested'," Mr Trump said.
Ms Frederiksen said the US remains one of Denmark's close allies.