Nicola Sturgeon accused Theresa May of sealing the fate of the United Kingdom after the prime minister rejected her demand for a second Scottish independence referendum before the Brexit talks conclude.
She said it would be wrong for there to be a vote until Scots could see the details of the Brexit deal she is about to start negotiating.
Sturgeon said on Thursday: "It's an argument for independence really in a nutshell, that Westminster thinks it has got the right to block the democratically elected mandate of the Scottish government and the majority in the Scottish parliament".
She also stated that the country needs to be "working together, not pulling apart".
The SNP leader is said to be considering applying for Scottish EFTA membership, which would allow entry to the European Union single market without being an European Union member.
Nicola Sturgeon responded to the Prime Minister's statement on Twitter, branding the move "undemocratic" and calling it proof that 'the Tories fear the verdict of the Scottish people'.
"If this Government are thinking for one minute of standing in the way of Scottish democracy, it will be the biggest recruiting sergeant possible for the cause of Scottish independence".
Prince William shows off his 'dad dance' skills
While many are always looking to find "dirt" or "gossip" on the royals it's nice that we can see them have a bit of fun. Prince William "dad-dancing"? Round our way that sort of thing is called fifteen-pints-and-a-couple-of-pills dancing.
She said that a refusal to allow a vote would mean that May's Tories were blocking the will of the Scottish people and afraid of their results.
Her comments raised tensions again with Scotland, whose first minister on Monday unexpectedly called for a new independence vote for the end of 2018 or spring 2019.
A day after rejecting Sturgeon's appeal by saying "now is not the time" for another plebiscite in Scotland, the premier will stress her commitment to the union between England, Wales, Scotland and Northern Ireland.
A separate Scotland faces spending years outside of the European Union single market even if it votes for independence, Iceland has warned.
"One last point - if PM thinks we won't know terms of Brexit by autumn next year, she must think her own timetable will fail".
"A referendum can not happen when the people of Scotland have not been given the opportunity to see how our relationship with the European Union is working", she said in a statement.
'What we have to do, as we did in 2014 but now in the different circumstances we face, is, before people are asked to make that choice, set out the process by which we secure our relationship with Europe. Polling expert John Curtice told Business Insider that doing so would cause a surge in support for independence and be "politically catastrophic". "We still hope they will step back from that vote".