Scotland voted to remain in the UK by a margin of 55 per cent to 45 per cent in a 2014 independence referendum that was billed as a once-in-a-generation event.
A new binding referendum requires the UK Government's approval, and Prime Minister Boris Johnson insists he will say no.
"The people of Scotland had a vote on this (in 2014), and they voted to remain part of the United Kingdom," Johnson spokesman Jamie Davies said today.
But Sturgeon's SNP, which leads the Government in Edinburgh, says Brexit has transformed the situation by dragging Scotland out of the European Union against its will.
A narrow majority of UK voters opted to leave the EU in a 2016 referendum, but a large majority in Scotland voted to stay.
Recent opinion polls suggest a majority of Scots now favour independence from the UK, with Brexit and the coronavirus pandemic boosting support for Scotland going its own way.
Sturgeon's calm, clear communication style during the pandemic has been widely praised, with many contrasting it to Johnson's more ramshackle approach — though the UK and Scottish governments have followed broadly similar public health policies, and both countries have seen high death tolls.
The whole of the UK has recorded more than 58,000 coronavirus-related deaths, the highest toll in Europe.
Sturgeon has not said what she will do if the UK government refuses to grant a referendum, though some pro-independence campaigners have suggested she could seek a ruling from the UK Supreme Court.
In an apparent reference to US President Donald Trump's fruitless efforts to overturn the result of the presidential election, Sturgeon said that "we are seeing across the Atlantic what happens to those who try to hold back the tide of democracy."
She added: "They get swept away".
- AP