Britain must renew its submarine-borne Trident nuclear weapons system if it is to maintain its "outsized" role in world affairs, US Defence Secretary Ash Carter said in comments published on Saturday.
A decision on replacing the ageing fleet of four submarines which carry nuclear warheads is due to be made this year and while Prime Minister David Cameron is committed to renewal, the issue has caused deep divisions in the opposition Labour Party.
The government has said replacing the submarines will cost 31 billion pounds while Reuters has puts the overall cost of renewing and maintaining a successor to Trident at more than 167 billion pounds ($234 billion) over 32 years.
Carter said the submarine fleet helped the "special relationship" Britain enjoyed with the United States, the BBC said on its website.
The deterrent allowed Britain to "continue to play that outsized role on the global stage that it does because of its moral standing and its historical standing," he was quoted as saying.
"It's important that the military power matches that standing and so we're very supportive of it. We depend upon the United Kingdom, the United Kingdom depends on us, that's part of the special relationship."
While most lawmakers in Cameron's party support keeping nuclear weapons, Labour leader Jeremy Corbyn, a veteran left-wing and anti-war activist, supports unilateral disarmament and is holding a review of the party's policy.
That has led to deep divisions among its lawmakers and earlier this week Labour's home affairs spokesman Andy Burnham said it might be impossible for the party to agree a position.