Nicola Sturgeon announced her intention to hold another vote on Tuesday
The British Prime Minister Theresa May has refused to agree to a second Scottish referendum before spring 2019, telling Nicola Sturgeon "now is not the time".
Mrs May says she will not start discussions with the Scottish First Minister on her proposals to hold a second independence vote when she is about to begin Brexit negotiations.
She said it would "not be fair" to expect the Scottish people when they did not know what the future partnership with the UK would be or "what an independent Scotland would look like".
Her refusal could escalate an already bitter war between Mrs May and Ms Sturgeon, who have already traded blows this week.
Ms Sturgeon announced plans to hold another vote on Scottish independence on Tuesday, just as it had been suggested Mrs May could officially trigger Brexit proceedings.
She said she had to take action because the UK government had "put up a brick wall" over Brexit negotiations, and was not listening to Scotland.
Mrs May accused her of "playing politics", saying on Thursday: "Right now we should be working together, not pulling apart.
"We should be working together to get that right deal for Scotland, that right deal for the UK as I say that's my job as prime minister and so for that reason I say to the SNP: now is not the time."
Ms Sturgeon will ask for permission to open discussions on a second referendum with Mrs May next week - but needs Westminster's permission to hold a vote.
The Scottish parliament could agree to hold a referendum anyway, but it would be advisory only and not legally binding.
However, a vote to end the 300-year union could put Mrs May in a very difficult position.