Pete Hegseth appeared to take a veiled swipe at Britain as he warned Nato allies that some countries would fail a forthcoming review of their military commitments unless they dramatically increase defence spending.

The US Defence Secretary used a meeting of Nato defence ministers to deliver a stark message that Washington would no longer shy away from publicly criticising allies it believes are not pulling their weight.

Arriving at Nato headquarters, Mr Hegseth said the United States would be “candid” with countries falling short of their obligations.

“I think that’s important, friends being honest with friends,” he said.

The comments came as the Pentagon launched a review of US military deployments in Europe, with Mr Hegseth suggesting some Nato members would emerge from the assessment favourably while others would not.

The intervention will be seen as a warning to Britain, where a fierce row over defence spending has exposed deep divisions at the heart of government.

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The crisis intensified after Defence Secretary John Healey and Armed Forces Minister Al Carns resigned following a dispute with Sir Keir Starmer and Rachel Reeves over the delayed Defence Investment Plan.

Mr Healey used a dramatic Commons statement to argue Britain must move far faster to strengthen its armed forces, warning that the international security environment was deteriorating at an alarming pace.

He urged ministers to increase defence spending to three per cent of GDP by the end of the decade, citing growing Russian aggression, instability in the Middle East, expanding Nato commitments and concerns over America’s future military posture in Europe.

“In the age of hard power and rising threats, this is not the moment for incremental change,” he told MPs.

The pressure on ministers increased further after Britain’s most senior military officer warned that funding shortages could force the Armed Forces to cut training exercises and operational activity.

Air Chief Marshal Sir Richard Knighton told peers that day-to-day military readiness was increasingly under threat unless additional resources were provided.

He warned that without an increase in funding, exercises, deployments and operational commitments would inevitably come under pressure.

The warnings come as Donald Trump continues to demand Nato allies dramatically increase military spending, pushing for a target equivalent to five per cent of GDP devoted to defence and security.

The US president has repeatedly accused European nations of relying too heavily on American military power while failing to adequately invest in their own armed forces.

Against that backdrop, Mr Hegseth’s comments will add to concerns that Britain risks finding itself in Washington’s crosshairs as questions grow over whether the Government is willing to match its defence ambitions with the necessary funding.

For Sir Keir Starmer, the message from both Nato and his former defence team is becoming increasingly difficult to ignore: in a more dangerous world, promises alone will not be enough.