The Prime Minister has warned Nicola Sturgeon now is "not a moment to play politics or create uncertainty", as a bitter Brexit battle broke out between the two.
Theresa May used an update in the House of Commons on Brexit to accuse the Scottish National Party of "constitutional game-playing" for calling a second independence vote.
The Prime Minister told MPs the people of Scotland didn't want a second referendum.
It was the latest in a series of blows exchanged by the two leaders over Ms Sturgeon's announcement on Monday of plans for a second referendum on Scottish independence, marking a significant escalation in hostilities.
Earlier the First Minister had questioned the Mrs May's legitimacy, telling her: "I was elected as FM on a clear manifesto commitment… The PM is not yet elected by anyone".
Ms Sturgeon said it was up to the Scottish parliament to decide when a vote would be held and warned Mrs May there should be "no blocking mechanisms".
She has called for a vote by spring 2019 on the grounds that by then voters would know what the Brexit deal was likely to bring.
However, the Prime Minister does not want to have to fight a campaign to keep the union together at a time she is carrying out negotiations with Brussels over Brexit.
She is understood to be preparing to reject demands for a vote within two years but leave the doors open for a vote after the Brexit deal is done.
The First Minister will see the approval of the Scottish Parliament for a new vote on independence next week although Mrs May would have to give approval.
The Prime Minister is expected to respond fully to Ms Sturgeon's plans once Holyrood has made its decision.
Mrs May also confirmed to MPs she would trigger Article 50 "before the end of the month" and it is expected she will not do this before 27 March.
There had been suggestions the Prime Minister would formally notify the EU the UK intended to leave on Tuesday, after the Brexit bill passed through Parliament.
However, she said: "We remain on track with the timetable I set out six months ago, and I will return to this House before the end of this month to notify when I have formally triggered Article 50 and begun the process through which the UK will leave the European Union."
SNP MPs Angus Robertson and Alex Salmond accused Mrs May of breaking her promise not to trigger Article 50 until she had an agreed UK-wide approach backed by Scotland.
The Prime Minister dismissed their claims saying her discussions with European leaders at the summit meeting last week had been on "jobs, growth and competitiveness", issues, she said, that were "relevant to Scottish people".
She added: "The most important single market to Scotland is the single market of the UK."
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%.