Nicola Sturgeon has opened fire on Theresa May over a second Scottish independence referendum by questioning the Prime Minister's legitimacy.
In a rapid escalation of hostilities between the two over Brexit and demands for a second independence vote, the Scottish First Minister hit back at Mrs May after suggestions the PM could delay a referendum.
She tweeted: "Trading mandates does not put PM on strong ground."
Setting the tone for the months ahead, she added: "I was elected as FM on a clear manifesto commitment re#scotref. The PM is not yet elected by anyone."
Mrs May accused the First Minister of "playing politics with the future of our country" after Ms Sturgeon ambushed her by setting out plans for a new vote on Scottish independence on Monday.
Ms Sturgeon 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.
But Mrs May replied that "a majority of (Scots) do not want a second independence referendum".
Ms Sturgeon called for a vote by spring 2019 on the grounds that voters would then be aware of the UK Government's full plans for Brexit and the deal it was likely to achieve with the EU.
The Prime Minister does not want to have to fight a battle on Scottish independence at the same time as she is carrying out the negotiations with Brussels over Brexit.
She is understood to be preparing to reject the demand for a vote within two years but leave the door open for a vote after the Brexit negotiations are completed.
The First Minister will seek the approval of Scottish Parliament for a new vote on independence next week but the governing Scottish National Party needs Westminster's approval to hold a referendum.
Ministers are said to be resigned to a second independence referendum but, according to The Times newspaper, Mrs May does not want it to take place within the next two years.
A Government source told the newspaper: "The Prime Minister has said this would mean a vote while she was negotiating Brexit and I think that can be taken pretty clearly as a message that this timing is completely unacceptable."
In 2014, Scotland voted to stay part of the UK by 55.3% to 44.7%; but in the Brexit vote Scots voted to remain in the EU by 62% to 38%.
If Scotland were to split from the UK it would have to apply for membership of the EU in its own right, which would mean joining the euro.
The application to join would also have to be supported by all 27 member states and a number of countries are unlikely to agree because of fears it would fuel separatism on their own doorsteps.
Spanish finance minister Alfonso Dastis said on Tuesday that Scotland would be "at the back of the queue".
The Prime Minister is expected to respond more fully to the referendum plans after it goes to the vote in Holyrood.
Polls since the Brexit vote have shown that support for Scottish independence has been relatively unchanged since the first referendum in 2014.
A Sky Data poll carried out after Ms Sturgeon's announcement on Monday found that Scottish voters also opposed holding a second referendum by 53% to 46%.
Ms Sturgeon announced her plans just hours before the Brexit bill cleared the House of Lords leaving Mrs May free to trigger Article 50 at any time.
There had been speculation that the Prime Minister could notify Brussels of the UK's intention to leave the EU on Tuesday but a Downing Street spokesman said it would not be until the end of the month.
Former UKIP leader Nigel Farage accused Mrs May of delaying because of the First Minister's referendum demand.
Labour leader Jeremy Corbyn said it was "wrong to hold another (referendum) so soon" and that the party opposed independence.
However, he added that Labour would not block a second referendum if the Scottish Parliament votes for it.
Scottish Conservative leader Ruth Davidson tweeted that Ms Sturgeon had "chosen the path of further division and uncertainty", while Lib Dem leader Tim Farron also said he opposed another vote.