A no deal Brexit would be "catastrophic" for Scotland and a "fundamental threat" to the UK, the Scottish Secretary has said.
Scottish and UK ministers met in London amid talk of a rebellion against Theresa May's EU withdrawal blueprint.
David Mundell said the only alternative to Mrs May's deal would be a "disastrous" exit without an agreement.
But the SNP say the UK staying in the single market and customs union would be a "straightforward compromise".
A draft withdrawal agreement thrashed out between officials from the UK and the EU was published last week, sparking resignations from Mrs May's cabinet and uproar among Eurosceptic backbenchers.
Some Tory MPs are threatening to hold a confidence vote in their party's leader, and opposition parties are also looking at ways to alter the deal or find a different compromise solution.
Mrs May is hosting a meeting with Scottish Conservative MPs and MSPs at Downing Street later.
Before that, representatives of the UK and devolved governments met in London for further talks on Brexit.
Brexit Secretary Mike Russell attended for the Scottish government, while his new UK counterpart Stephen Barclay and Mr Mundell were there for the UK government.
Despite initial speculation that he might resign from the cabinet, the Scottish secretary told BBC Radio Scotland that he was backing the prime minister's plan.
He said: "I'm supporting the deal because I believe a 'no deal' outcome would be catastrophic for Scotland. I believe it would be a fundamental threat to the continuation of the United Kingdom and therefore in the round you have to weigh up all the issues. These are difficult and complex judgements but I'm not prepared to countenance a no deal outcome for Scotland.
"Everyone is clear it's not a perfect deal. It's not as bad a deal as characterised. It contains many positive elements in relation to the rights of EU citizens.
"Going forward it contains this hugely important prospect for Scottish businesses for being able to trade in the EU without tariffs, without quotas - that's the number one thing that businesses have said that they want."
Mr Mundell also claimed that the SNP's plans to vote against the deal were motivated by their hunger for independence.
He said: "That's why Nicola Sturgeon is so keen on it, that's why she's mandating her MPs to vote for a no deal Brexit, because she understands that the chaos and disruption that a no deal Brexit would bring would be the best recruiting base for her independence referendum."
The SNP has also spoken out repeatedly against a no deal Brexit, with party leader and First Minister Nicola Sturgeon insisting that UK ministers are presenting a "false choice" between a "bad deal and no deal".
She argues that rejecting Mrs May's plan would open up the possibility of a third way forward, and wants the UK to remain within the EU's single market and customs union.
On Sunday, she said that MPs supporting the withdrawal agreement as it stands would be "deeply irresponsible", and said she would be heading for London with talks with Labour's Jeremy Corbyn and other opposition leaders to discuss plans for a "clear alternative".
'Responsible thing to do'
Stephen Gethins, the SNP Europe spokesman at Westminster, told the BBC's Good Morning Scotland programme that opposition parties should work together to come up with a new plan.
He said: "Right now we're in a parliament of minorities and as we know from Holyrood and from normal European legislatures, that often the government doesn't have a majority and you need to talk to each other.
"This doesn't seem to have dawned on the government yet, who look less and less likely to get their deal through, so I think it's the responsible thing to do and something we've been trying to do all along this process."
Mr Gethins added: "We have set out a compromise which is remaining part of the single market in the customs union which is, incidentally, a really straight-forward compromise because it's basically the deal you've got inside the transition period.
"What we need to do it sit down and look at a least-worst option to get a way out of this and I very much look forward to speaking to Labour colleagues to try and make some progress on this.
"You've got a government right now, during peacetime, that's stockpiling foods and medicines, that's talking about the army having to be deployed on the streets.
"That is a level of colossal political failure and political crisis we haven't seen for decades and that's why it's right for politicians to be talking to each other and that why it's right for Nicola Sturgeon to be coming down to London this week."
Labour's Shadow Scottish Secretary Lesley Laird also said the UK government was presenting MPs with a "false choice" on Brexit.
She said: "Theresa May once believed that no deal was better than a bad deal. Now David Mundell is saying the exact opposite, yet sees no conflict with his position in cabinet."