Donald Trump’s administration has hit out at Nato allies for "lagging behind" in their commitments to boost their defence spending, ahead of a key summit this week.
The White House has warned of consequences if allies do not "immediately” fulfil their pledge to increase their military spending to 5% of GDP by 2035.
Britain's pledge so far stands at 2.7% after Sir Keir Starmer announced a £15 billion upgrade to the country's armed forces last week, The Telegraph reports.
It puts the UK and the US on a potential collision course at the Nato summit, which commences in Ankara, Turkey, on Tuesday.
On Sunday night, US ambassador to Nato Matt Whitaker said: “Some allies are doing more than others. Poland, the Nordic countries, the Baltic countries lead the way.
“But many others are lagging behind, and President Trump expects all allies to step up immediately and not only get on a sustainable path to the 5 per cent but to get to 5 per cent as soon as possible.”
It is thought higher defence spending may give countries priority when they seek to purchase US weaponry, as well as easier access to Trump himself.
Analysts say this is part is the president's plan to reward or punish nations depending on whether they choose to boost their defence spending.
Failure to reach the 5% target could lead to a "less capable Europe and Canada", according to US officials.
Last month, US defence secretary Pete Hegseth announced a review of American military forces in Europe as he questioned if some members were meeting their spending commitments, claiming they still seemed “to think the era of free-riding is here”.
Keir Starmer’s plan to hike defence spending by £15 billion is also under scrutiny, with Downing Street unable to say exactly where the cuts required to pay for the increase will come from, with around a third deferred to the next budget.
Even with the latest increase, former defence secretary John Healey – who quit in protest at the level of extra military funding being offered – said the UK would be spending 2.7% of economic output on defence in 2030.
He stressed the need to “develop a clear, credible funding plan” to ensure the UK met its Nato commitment to spend 3.5% of gross domestic product (GDP) on core defence by 2035.
