Nicola Sturgeon said it was "democratically unacceptable" that Scotland faced the prospect of being taken out of the EU against its will. She said the Scottish government would begin preparing legislation to enable another independence vote.
Scotland voted in favour of the UK staying in the EU by 62% to 38%. The UK as a whole has voted to leave, by a margin of 52% to 48%, prompting UK Prime Minister David Cameron to announce he would stand down by October. The SNP manifesto for May's Holyrood elections said the Scottish Parliament should have the right to hold another referendum if there was a "significant and material change" in the circumstances that prevailed at the time of the 2014 referendum, such as Scotland being taken out of the EU against its will.
At a news conference in Edinburgh, Ms Sturgeon said: "It is, therefore, a statement of the obvious that a second referendum must be on the table, and it is on the table," she said. The Scottish government's resilience committee, which meets in times of emergency, is due to meet on Friday afternoon. Ms Sturgeon said the Scottish cabinet would meet on Saturday and she would make a statement to MSPs on Tuesday.
The first minister said there was now a significant divergence between Scotland and the rest of Britain which she "deeply regretted". A majority of voters in all 32 council areas in Scotland voted Remain. Speaking at her official residence, Bute House, she said: "I intend to take all possible steps and explore all possible options to give effect to how people in Scotland voted - in other words to secure our continuing place in the EU, and in the single market in particular."
Asked if there were any other options available to the Scottish government, she replied: "I think an independence referendum is now highly likely but I also think it is important that we take time to consider all steps and have the discussions, not least to assess the response of the European Union to the vote that Scotland expressed yesterday."
Ms Sturgeon said: "After a campaign that has been characterised in the rest of the UK by fear and hate, my priority in the days, weeks and months ahead will be to act at all times in the best interests of Scotland and in a way that unites, not divides us.
"Let me be clear about this. Whatever happens as a result of this outcome, England, Wales and Northern Ireland will always be Scotland's closest neighbours and our best friends - nothing will change that. "But I want to leave no-one in any doubt about this. I am proud of Scotland and how we voted yesterday.
"We proved that we are a modern, outward looking and inclusive country and we said clearly that we do not want to leave the European Union "I am determine to do what it takes to make sure these aspirations are realised."Scottish Conservative leader Ruth Davidson said she shared Nicola Sturgeon's disappointment at the result - but she did not believe it justified holding another independence referendum.
In a statement she 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 today. "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.
"The 1.6 million votes cast in this referendum in favour of remain, do not wipe away the 2 million votes that we cast less than two years ago. "And we do not address the challenges of leaving the European Union by leaving our own Union of nations, our biggest market and our closest friends. "I believe in Scotland's place within the United Kingdom today as much as ever."