Theresa May accused Green MP Caroline Lucas and some Labour MPs of defending the country's enemies, as MPs prepare to vote on renewing Trident.
The MP for Brighton Pavilion had said the UK's nuclear weapons are "driving proliferation - not the opposite", before the prime minister rejected the suggestion, saying: "I have to say to you that sadly you and some members of the Labour Party seem to be the first to defend the country's enemies and the last to actually accept the capabilities that we need."
Mrs May said it is "a great pity" that members of the Labour front bench "fail to see the necessity" of Britain's nuclear deterrent "given that the Labour party in the past has put the British national interest first in looking at this issue."
Speaking in the Commons, the prime minister added that we "cannot afford to relax our guard" and "need to be prepared to deter threats to our lives and our livelihoods."
Another Scottish independence referendum is fast approaching, SNP warns, after Westminster voted to renew Trident.
Labour MPs reacted angrily after Jeremy Corbyn referred to the party's policy on the UK's nuclear deterrent in the past tense.
Nicola Sturgeon has accused the UK Government of "playing games" over Trident, ahead of MPs voting on the renewal of the nuclear deterrent.