Scotland's first minister has called on Boris Johnson to rule out a no-deal Brexit as she repeated her "profound concerns" about the prospect of him leading the country.
Nicola Sturgeon said Mr Johnson should be in no doubt about the gravity of the situation he is about to inherit as PM.
And she pledged to work with other parties to "stop Brexit and block a no-deal Brexit".
Her statement came just minutes after Mr Johnson was elected as Tory leader.
The former London mayor will succeed Theresa May as prime minister on Wednesday after defeating Jeremy Hunt by 92,153 votes to 46,656 in the ballot of Conservative Party members.
In his victory speech, Mr Johnson promised he would "deliver Brexit, unite the country and defeat Jeremy Corbyn".
He has previously insisted that he is "not aiming for a no-deal outcome" for Brexit - but has also pledged that the UK will be leaving the EU on 31 October "deal or no deal".
In her statement, Ms Sturgeon congratulated Mr Johnson on his victory in the leadership contest, and said she would do "everything possible to ensure that he respects Scotland's views and interests".
She added: "However, I have profound concerns about the prospect of his premiership and it would be hypocritical not to be frank about these.
"These are concerns that I am certain will be shared by the vast majority of people in Scotland who, had they been given any say, would not have chosen to hand the keys of Number 10 to someone with his views and track record.
"Mr Johnson should be in no doubt about the gravity of the situation he is about to inherit as prime minister nor, in particular, about the strength with which I and others will oppose his threat of a no-deal Brexit".
1. Congratulations to Boris Johnson on his election as leader of the Conservative Party. Despite our many differences, I will do all I can to develop a way of working with him that respects and protects Scotland’s views and interests.— Nicola Sturgeon (@NicolaSturgeon) July 23, 2019
Reacting to the news, Scottish Conservative leader Ruth Davidson said that Mr Johnson would face an "enormous task" as prime minister at an "incredibly challenging time".
She congratulated her fellow Tory on his victory, despite having backed his rival Jeremy Hunt.
Ms Davidson said her priority was to make sure that Mr Johnson "will deliver for Scotland within the UK".
New PM's political honeymoon is already over
Analysis by BBC Scotland Political Editor Brian Taylor
In terms of intent, of political pitch, Mr Johnson's acceptance speech probably hit the right, temporary note. Void of content. Heavy on rhetoric.
Giving the immediate audience what they wanted to hear. Brexit? A dawdle. Corbyn? Ancient history. UK unity? Leave it to B.
After the agonies of Theresa May's uncertain leadership - which followed a catastrophic election campaign in 2017 - the Tories want robust reassurance, not timid acquiescence. They want Churchill, not Chamberlain.
Mr Johnson is many things. But he is not daft. He knows - he knows - that he faces a huge problem to deliver Brexit, especially by the target date of Hallowe'en.
A problem to strike a deal with a reluctant and increasing fractious and bored EU. A problem to steer a no-deal departure - which he insists he doesn't want - past a determined, if divided, Commons.
Energy there will be. But energy may not be enough.
The first minister claimed that any form of Brexit would be "deeply damaging" to Scotland and the rest of the UK.
And she said that Mr Johnson's commitment to leaving by 31 October regardless of whether an exit deal had been agreed "flies in the face of logic, common sense or any basic regard for the wellbeing of the people and nations of the UK".
Ms Sturgeon added: "It is a deeply irresponsible threat, and not one that should be contemplated by any serious political leader. It should now be taken off the table without delay or equivocation."
She promised that the Scottish government, and SNP MPs at Westminster, would be at the forefront of any and all moves to oppose Brexit, and in particular a no-deal Brexit.
The first minister said: "We will be joined in those efforts by others from across the political spectrum - and the fact that Mr Johnson already faces strong opposition from members of his own party who oppose a no-deal Brexit underlines the seriousness of the position he finds himself in.
"Scotland did not vote for Brexit, or for the current Tory government - and certainly not for Boris Johnson as prime minister. All of this underlines the need for Scotland to have the right to determine our own future, in line with the democratic wishes of all those who live here."