Nicola Sturgeon has said she wants to hold a second referendum on Scottish independence by 2021 if the country is taken out of the EU, the BBC says.

The first minister told Holyrood that she would introduce legislation soon to set the rules for another vote.

But she indicated that she would need the agreement of the UK government before actually holding a referendum.

Downing Street has previously said it will not grant a new Section 30 order, which underpinned the 2014 referendum.

Sturgeon claimed this position was "unsustainable" and challenged her party to increase support and demand for independence.

But the prime minister's official spokesman said: "As we have been repeatedly clear, Scotland has already had an independence referendum in 2014 and voted decisively to remain in the United Kingdom. This should be respected. Our position hasn't changed."

Sturgeon has faced calls from some within the SNP - which will hold its conference at the weekend - and the wider independence movement to hold a referendum sooner rather than later.

She told MSPs that to "rush into an immediate decision before a Brexit path has been determined would not allow for an informed choice to be made" about the future.

However, the first minister added: "If we are to safeguard Scotland's interests, we cannot wait indefinitely.

"That is why I consider that a choice between Brexit and a future for Scotland as an independent European nation should be offered in the lifetime of this parliament.

"I can confirm that the Scottish government will act to ensure that the option of giving people a choice on independence later in this term of parliament is progressed."

The next Scottish Parliament election is due to be held in May 2021.