LONDON, Jan. 14 (Xinhua) -- Scottish First Minister Nicola Sturgeon hit back at British Prime Minister Boris Johnson on Tuesday after he rejected paving the way for a new independence referendum for Scotland.

Prime Minister Johnson has written to the Scottish National Party l(SNP) leader saying that she and her predecessor Alex Salmond had made a personal promise that the first referendum in 2014 would be a once-in-a-generation vote.

Scottish voters backed remaining as part of the UK by 55 to 45 in the 2014 referendum.

"I cannot agree to any request for a transfer of power that would lead to further independence referendums," Johnson said.

He said a further independence referendum would continue the political stagnation that Scotland has seen for the last decade.

"It is time we all worked together to bring the whole of the United Kingdom together and unleash the potential of this great country," Johnson told Sturgeon.

In Edinburgh, Sturgeon said Johnson's formal refusal of her request for a referendum to be held later this year was predictable but also unsustainable and self-defeating.

She insisted that Scotland will have the right to choose.

Responding to Johnson's letter, Sturgeon said: "They know that given the choice the overwhelming likelihood is that people will choose the positive option of independence."

"It is not politically sustainable for any Westminster Government to stand in the way of the right of the people of Scotland to decide their own future and to seek to block the clear democratic mandate for an independence referendum," she added.

Sturgeon said she would set out the SNP administration's next move later this month and it would also ask the Scottish Parliament to endorse Scotland's right to choose.

Sturgeon's renewed demand for a fresh independence referendum was given a boost when the SNP made significant gains in last month's general election. The party won 48 of Scotland's 59 seats at Westminster.

Last month an opinion poll published in The Times showed support for Scottish independence had fallen. The new YouGov poll suggested 56 percent of respondents would say no to Scotland breaking away from the UK, with 44 percent wanting the split.

A previous YouGov poll carried out for The Times last September showed 49 percent in favor of independence and 51 percent against.

The latest figure shows more people are opposed to Scotland going it alone than in the 2014 referendum.