An independent Scotland would require the unanimous backing of all Nato members if it wants to join the Western alliance, the organisation's secretary general has made clear.

Anders Fogh Rasmussen said that any newly independent state that wanted to become a Nato member would have to apply to join and then gain the support of all 28 existing member states.

"If a new independent state wants to become a member of Nato it will have to apply for Nato membership," he told the Carnegie Europe think tank in Brussels.

"Such an application will be addressed in exactly the same way as all applications are dealt with. Eventually it will require consensus - unanimity - within the alliance to accept a new member of our alliance."

The SNP says that it supports Nato membership provide it is not required to retain the Trident nuclear deterrent - currently based at Faslane on the Clyde - on Scottish soil.

Mr Rasmussen insisted there had been no discussion within the alliance regarding any application by an independent Scotland to join, describing it as a "hypothetical question".

He refused to be drawn on how long it would take for such an application to be dealt with, saying that it would depend on an applicant country's ability to fulfil the "necessary criteria".

Mr Rasmussen dismissed suggestions that a Yes vote in the referendum would weaken the UK's ability to contribute to Nato.

"I don't see that any outcome of the Scottish referendum will have an impact on the UK's contribution to Nato," he said.

An SNP spokeswoman said: "The Nato secretary general has simply outlined the process we are already aware of.

"Former UK ambassador to Nato Dame Mariot Leslie - who is voting Yes this Thursday - has made it clear she believes that the Nato allies 'would see it in their interests to welcome and independent Scotland into Nato'.

"We have made clear that, following a vote for independence, the Scottish Government will notify Nato of our intention to join the alliance and negotiate a transition from membership as part of the UK to independent membership, taking our place as one of the many non-nuclear members.

"Nato's own stated intention is for membership to be open to all European democracies that meet the membership criteria - and given that Scotland occupies a key strategic location in the North Atlantic, we believe our continued membership will be in the strong interests of the rest of the alliance."