David Cameron has defended the political union between Scotland and England, urging voters north of the border to reject independence in exchange for more powers.
The Prime Minister did not explain what the powers could be, but argued that the major decision on whether Scotland should leave the Union must be settled first.
First Minister Alex Salmond immediately hit back, warning that Scots "won't be fooled" by the offer, which Mr Cameron made for the first time on Thursday.
In a keynote speech in Edinburgh, Mr Cameron said: "When the referendum on independence is over, I am open to looking at how the devolved settlement can be improved further. And, yes, that does mean considering what further powers could be devolved.
"But that must be a question for after the referendum, when Scotland has made its choice about the fundamental question of independence or for the United Kingdom."
He held out the prospect of more powers for the Scottish Parliament just hours before meeting Mr Salmond, the Scottish National Party leader, for talks on the staging of the independence referendum.
The PM was forced to use a side door at the Scottish Government's St Andrew's House headquarters because of a demonstration by anti-cuts protesters outside. After the talks, Mr Salmond identified the issue of whether there should be one or two questions on the ballot paper as a major stumbling block.
Mr Salmond said the Prime Minister must explain his new offer. He said Scotland had been in a similar scenario, recalling that in the run-up to the 1979 devolution referendum MP Sir Alec Douglas-Home had said a Tory government would introduce a better Scottish Assembly.
Mr Salmond said: "What happened then was 17, 18 years of no deal at all from the Conservative government at Westminster."
The First Minister added: "The shadow of Sir Alec Douglas-Home I think is cast very large over this. What's the old saying: 'fool me once, shame on you, fool me twice shame on me'. Scotland, I don't believe, will be fooled twice."