Scotland is on course for a second independence referendum in the next the next two years.
Nicola Sturgeon said another vote on separation was “highly likely” after the UK voted to Leave the EU, but Scotland unanimously voted to Remain.
The First Minister said her government was already working on drafting the necessary legislation to call another vote on the future of the UK.
Scottish Conservative leader Ruth Davidson said a second vote on separation will not “help us achieve the stability” required after the Leave vote.
The SNP manifesto for the Holyrood election suggested that a “significant and material change in circumstance”, such as “Scotland being taken out of the UK against our will”, would be a trigger for a second independence referendum.
All 32 Scottish local authorities backed staying in the EU after Thursday’s vote, as did a majority in Northern Ireland, but England and Wales backed Brexit.
Ms Sturgeon told an audience at Bute House: “There is a significant and material change in circumstances and it is therefore a statement of the obvious that the option of a second referendum must be on the table – and it is.”
The First Minister said “all options” are being considered in a bid to protect Scotland’s membership of the EU.
The SNP leader will be speaking to EU Commission officials, as well as other European leaders, to make clear Scotland “does not want to leave” the Brussels bloc.
She added: “It would not be right to rush to judgement ahead of discussions on how Scotland’s result will be responded to by the EU.
“However, when the Article 50 process is triggered (the mechanism for leaving the EU) in three months time the UK will be on a two-year path to the EU exit door.
“If parliament judges that a second referendum is the best or only way to protect our place in Europe, it must have the option to hold one within that timescale.
“That means we must act now to protect that position.
“I can confirm that we will begin to prepare the legislation that will be required to enable a new independence referendum to take place if and when parliament so decides.”
When asked what options other than a second independence referendum were available to keep Scotland in the EU, Ms Sturgeon said: “I think another independence referendum is now highly likely.
“But I also think it is important that we take time to consider all steps and to have discussions not least to assess the response of the European Union to the vote that Scotland expressed yesterday.”
While the SNP is now a minority government, there remains a pro-independence majority at Holyrood, with the Scottish Green’s also favouring separation.
But, speaking in Edinburgh yesterday, Tory leader Ms Davidson said: “Like the First Minister I want to see stability prioritised in the days ahead.
“Scotland will open for business next week in the same way as it closes (on Friday).
“But I do not believe that a second independence referendum will help us achieve that stability nor that it is in the best interests of the people of Scotland.”