Labour will not scrap Trident or leave Nato, shadow foreign secretary Hilary Benn has insisted.
New leader Jeremy Corbynopposes the replacement of the nuclear weapons system and has questioned the role of the international military alliance.
But Mr Benn said Nato was the "conerstone of our security" and insisted he did not see Britain withdrawing.
He told BBC One's Andrew Marr Show: "My view is that we need to maintain an independent nuclear deterrent."
He added: "We live in a differently dangerous world now. We need a continuous at sea deterrent. We need to do it in the most cost effective way and that is the view which the Labour party, including the Labour party conference has taken for many years."
Asked if he could serve in the shadow cabinet if the party voted to leave Nato and get rid of Trident, he replied: "I don't think that is going to happen."
Senior Labour figures have privately pledged support for airstrikes in Syria with half of Mr Corbyn's shadow cabinet ready to back intervention, according to the Sunday Times.
It names Mr Benn as one of the key figures ready to back the Government if a coherent plan to tackle Islamic State is put forward.
Pressed over whether he would support action, he told the programme: "We have said, consistently, if the Government has a proposition we need to look at what that is."