Nicola Sturgeon has said Boris Johnson is a pursuing a "dangerous" no-deal Brexit after she met with the prime minister in Edinburgh.
Scotland's first minister also said there was no clarity on how he planned to reach an exit deal with the European Union, which has repeatedly said it will not renegotiate the withdrawal agreement it reached with his predecessor Theresa May.
Ms Sturgeon continued: "That makes me think that whatever Boris Johnson might be saying publicly about his preference being to strike a deal, in reality he is really pursuing a no-deal Brexit because that is the logic of the hardline position that he has taken.
"I think that is extremely dangerous for Scotland, indeed for the whole of the UK."
Ms Sturgeon also said Mr Johnson's Brexit strategy of hoping the EU will renegotiate a new withdrawal deal is "doomed to failure".
She continued: "The only strategy or tactic that you can get from it is that he thinks the EU is going to blink.
"Having had many tortuous meetings with his predecessor on the issue of Brexit, I think that for a long period of time that's what she thought as well.
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"The EU – whether you think this is a good thing or a bad thing – has been very consistent in the position it's taken. It's been very united and if you're pinning your entire strategy on a belief that's suddenly going to change, then I think it's a strategy that's doomed to failure.
"Or it's a strategy that is destined to fail because you actually want the alternative, which is a no-deal Brexit."
The Scottish National Party leader was speaking after meeting with Mr Johnson during his first trip to Scotland as prime minister.
Ms Sturgeon also said that whatever happens over Brexit will have an impact on the decision about the timing of a second Scottish independence referendum.
She added it was not democratic to block the right of the people of Scotland to choose.
A Downing Street spokesman said of the meeting: "The prime minister said he was a passionate believer in the power of the union and he would work tirelessly to strengthen the United Kingdom and improve the lives of people right across Scotland."
The statement added: "On Brexit, the prime minister said that while the government's preference is to negotiate a new deal which abolishes the anti-democratic backstop, the UK will be leaving the EU come what may."
Mr Johnson also met with Scottish Conservative leader Ruth Davidson while in Scotland. She said she won't support leaving the EU without an agreement.
While the UK as a whole voted to leave the EU in 2016, Scotland backed Remain by a large margin.
Mr Johnson's meeting with Ms Davidson may have been tense as he ignored her advice to keep David Mundell in his role as Scottish secretary, sacking him and replacing him with Alister Jack.