He made the comments as he pledged his government would publish a long-delayed defence investment plan before next month's NATO summit.

"It is our intelligence assessment and the assessment of other countries in NATO that there could be an attack by Russia on NATO as soon as 2030," Starmer said.

"So you can see the urgency and the priority that we're putting behind this now," he added during a visit to a drone manufacturer in southwest England.

It echoes similar timeframes expressed by other European leaders and NATO chief Mark Rutte who warned in December that Russia "could be ready to use military force against NATO within five years".

Starmer has pledged to raise defence spending to 2.5 percent of gross domestic product from next year, increasing to three percent in the next parliament.

A 10-year defence investment plan following a review of the UK's defence capabilities was meant to be published late last year but has not yet been produced.

Starmer announced it would be published before the NATO summit in Turkey, beginning on July 7.

UK media has reported that the plan has been delayed due to disagreement between the finance ministry and other departments over the cost.

Starmer insisted to reporters it would be "fully funded".

Earlier Friday, Britain's military chief warned that Britain must boost its defences in response to threats posed by Russia, which invaded Ukraine more than four years ago.

"In my 35-year career, this is the most dangerous period that I have known," Air Chief Marshal Richard Knighton told the BBC.

"And as a consequence, it is important that we enhance the capability and the readiness of our armed forces alongside our allies to deter our adversaries from doing something daft."

US President Donald Trump has repeatedly urged NATO countries to spend more on defence and become less reliant on Washington for security.