NATO leaders have rejected a rise in defence spending to 4 percent of GDP, opposing a demand of U.S. President Donald Trump who had earlier called on NATO countries to spend as much as 4 % of their GDP on defence, and upgrading of their military forces.

Trump told the NATO leaders on Wednesday that they should up their defense spending to 4 percent of their countries' economic output, which is higher than the pledged 2 percent. Trump also tweeted that the NATO members should give 2 percent to defence immediately and not only as of 2025.

But virtually all NATO leaders were united in rejecting Donald Trump's demand.  The Czech Republic's Deputy prime minister,  Jan Hamacek , said he considered 2 percent of GDP an optimal level of defence spending.

Many NATO leaders rejected Trump's demand outright, dismissing the idea of  increasing defence expenditure to 4 percent of GDP by 2021. A number of NATO leaders who had gathered in Brussels called the idea "a pure fantasy".

Meanwhile, NATO allies have cast doubt on US President Donald Trump's claim they had pledged to "substantially" raise their defence budgets, saying they simply remained committed to a 2014 deal.

NATO chief Jens Stoltenberg told US broadcaster CNN the allies had "a commitment to spend 2%" of their annual output (GDP) on defence budgets.

Members agreed four years ago they would all reach that target by 2024.

Italy's new Prime Minister, Giuseppe Conte, Canadian Prime Minister Justin Trudeau and French President Emmanuel Macron also made it clear they had not signed up to anything more than what was agreed four years ago -- that is spending  2%  of their annual output (GDP) on defence.

French president, Emmanuel Macron, also rejected Trump's demand for a substantial increase in defence spending. Speaking at the NATO summit in Brussels, Macron said:  "Everyone agreed to raise spending, in line with commitments made in 2014.  I am unconvinced by proposals to increase defence spending  to 4% of GDP."