Those questioning the Scottish Government's mandate to hold a Scottish independence referendum risk "undermining the democratic process", the First Minister has said.

Nicola Sturgeon issued the warning in her opening remarks to MSPs in a debate about holding a fresh independence vote between autumn next year and spring 2019.

The SNP was elected to form the Scottish Government last year on a manifesto which set out the right of the Scottish Parliament to hold a referendum if the UK as a whole voted to Leave the EU but Scotland voted to Remain.

Sturgeon said there is an "unquestionable democratic mandate" for a second independence referendum.

The SNP leader said: "The suggest that an emphatic election victory on the basis of a clear manifesto commitment and a parliamentary majority on an issue does not provide a mandate begs the question what does? And it runs the real risk of undermining the democratic process."

The motion calls on the Scottish Parliament to endorse "the sovereign right of the Scottish people to determine the form of government best-suited to their needs" and "mandate the Scottish Government to take forward discussions with the UK Government" on the details of a section 30 order".

A section 30 order to temporarily devolve the power to Holyrood to hold a referendum must take place before one can be held.

Scottish secretary David Mundell has said the UK Government will not enter into any such discussions until the country leaves the European Union and it will reject any request.

Sturgeon told MSPs: "Let me make this clear - if the UK Government disagrees with that timeframe, then they should set out a clear alternative and the rationale for it.

"As I have said in recent days, I am, within reason, happy to have that discussion to see if we can find common ground that I can then propose to this parliament."

The SNP is being backed in its plans for a fresh referendum by the pro-independence Scottish Greens.

Green co-convener Patrick Harvie said: "It is absurd to suggest that we should not respond to and react to the fundamentally-changed circumstances we now find ourselves in."

He added: "The situation is changed not only by the EU referendum result, but by everything the UK Government has done with it.

"The recklessness of holding that referendum to resolve their own internal squabbles, the utter lack of a plan ... and the disrespect shown to Scotland since then."

Scottish Conservative leader Ruth Davidson said her move to hold a second referendum shows her top priority is "separation not education".

She said: "The people of Scotland don't want this and it won't wash to have a First Minister standing there, washing her hands, saying 'It's not me that's dragging us there, it's with a heavy heart, a big Tory did this and ran away'.

"It won't do, First Minister, take responsibility."

Scottish Labour leader Kezia Dugdale said her party will back the union in any future referendum.

Dugdale said: "I believe in the United Kingdom not as a symbol of past glories or purest ideology, but as a living, breathing union of nations that delivers for the people of Scotland.

"The pensioners, whose income is secured through a UK state pension and benefits system. The shipyard workers, who are in jobs because of UK defence contracts.

"The staff in East Kilbride, who deliver aid to some of the poorest countries in the world on behalf of us all.

"The schools that are built because of the extra money we receive by being in the UK.

"The NHS that we built together that is sustained because we pool and share our resources across the whole of Britain."

Scottish Liberal Demcorat leader Willie Rennie also spoke out against the SNP's plans.

He said: "Division with Europe is not resolved by division in the UK. The response to hard Conservative Brexit is not hard SNP independence.

"We do not mount chaos onto chaos of Brexit with the chaos of independence. We do not respond with a break from Europe with a break from the UK."

The SNP's motion is expected to pass with the support of Green MSPs when it is voted on by MSPs on Wednesday evening at Holyrood.

You can watch MSPs debate the motion live on the STV Player: