Scotland's leader on Monday said she would seek authority for a new independence referendum because Britain is dragging Scotland out of the European Union against its will.

Scottish First Minister Nicola Sturgeon demanded an independence referendum to be held in late 2018 or early 2019, once the terms of Britain's exit from the European Union have become clearer.

A vote that could rip apart the United Kingdom just months before Brexit adds a tumultuous twist and highly uncertain consequences to the two-year process of leaving the EU after more than four decades.

"If Scotland is to have a real choice - when the terms of Brexit are known but before it is too late to choose our own course - then that choice must be offered between the autumn of next year, 2018, and the spring of 2019," Sturgeon told reporters.

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Her demand comes just as British Prime Minister Theresa May is poised to launch the Brexit process, something opposed by most Scots in last June's vote on leaving the bloc.

Ultimately it is the UK parliament in Westminster - where May commands a majority - which makes the call on whether Scotland can hold a second referendum. But if May refused to approve such a vote she could provoke a constitutional crisis.

May's government said in response to Sturgeon's announcement that it is seeking "a future partnership with the EU that works for the whole of the United Kingdom. The UK government will negotiate that agreement, but we will do so taking into account the interests of all of the nations of the UK."

The British government didn't say whether it would give approval, but said an independence ballot "would be divisive and cause huge economic uncertainty at the worst possible time".

This month, May accused Sturgeon's Scottish National Party of sacrificing not only the United Kingdom but also Scotland with its "obsession" with securing independence.

Sturgeon has previously said she wanted Scotland to be allowed to strike its own deal with the EU to keep access to the bloc's tariff-free single market. But on Monday she said her efforts had hit a "brick wall of intransigence" in London.

"If the UK leaves the EU without Scotland indicating beforehand - or at least within a short time after it - that we want a different relationship with Europe, we could face a lengthy period not just outside the EU but also the single market," she said.

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Al Jazeera's Barnaby Phillips, reporting from London, said it remains to be seen how the battle over a new vote unfolds for Sturgeon in the coming weeks.

"You could expect quite a political fight over the timing of such a referendum, over the wording of such a referendum," said Phillips. "The initial response from Teresa May and from Downing Street has been quite damning. They are saying that this is divisive."

The results of the June 23 Brexit referendum called the future of the UK into question because England and Wales voted to leave the EU but Scotland and Northern Ireland voted to stay, with an overall 55 percent in favour of leaving.

Scots rejected independence by 55-45 percent in a referendum in September 2014, though the vote energised Scottish politics and support for the SNP has surged since then.

Sterling rose after Sturgeon said the earliest date for a new Scottish independence referendum was in the autumn of next year. British government bond prices fell.

Recent opinion polls have shown support for independence running at close to 50 percent.

At her news conference on Monday, Sturgeon was asked if she believed she could win a second independence vote. "Yes I do. Absolutely, I believe that."