Scotland should hold an independence referendum before the current Scottish parliamentary term ends in May 2021, First Minister Nicola Sturgeon said on Wednesday.
"A choice between Brexit and a future for Scotland as an independent European nation should be offered in the lifetime of this parliament," Sturgeon told Holyrood, Scotland's devolved parliament.
She said she would prepare legislation before the end of 2019 for this to happen.
Scotland, part of the United Kingdom for more than 300 years, rejected independence by 55-45 in a 2014 referendum.
However, for a second referendum to take place, Sturgeon admitted she would need the agreement of the UK Government.
And in response to Sturgeon's speech, a spokesman said British Prime Minister Theresa May's view was that the majority of voters rejected leaving the rest of the UK in the 2014 referendum, and that result should be respected.
"I can confirm that the Scottish Government will act to ensure that the option of giving people a choice on independence later in this term of parliament is progressed," she told MSPs.
Following her statement, Conservative, Labour, and Liberal Democrat MSPs spoke to criticise Sturgeon's call for a second referendum.
Differences over Brexit have strained the UK. Scotland and Northern Ireland voted to stay in the EU in a 2016 referendum, while Wales and England vote to leave.
- This article was amended to correct the result of the 2014 Scottish independence referendum.