Nicola Sturgeon has branded Prime Minister Boris Johnson a "scaredy-cat" after he said he would never face her on a televised debate.
Ms Sturgeon, the SNP leader, has been excluded from Tuesday evening's ITV debate between Mr Johnson and Labour leader Jeremy Corbyn.
Mr Johnson said ahead of the debate that he would only debate with "serious candidates" to become prime minister.
But Ms Sturgeon said she was willing to face the PM "any time, any place".
A joint legal challenge by the SNP and Liberal Democrats to be included in the ITV debate was rejected by the High Court on Monday.
Speaking to newspaper reporters after the decision, Mr Johnson accepted that the SNP could be "very influential" in British politics.
But he said he would only agree to debate Ms Sturgeon if she "takes leadership of her party in Parliament and is a serious contender to be prime minister of the UK".
Mr Johnson added: "The candidate to be prime minister who Nicola Sturgeon would support is Jeremy Corbyn and that is why he is the appropriate person (to debate)".
Ms Sturgeon, who is Scotland's first minister and is not standing to become an MP, argued that a debate between the Labour and Tory leaders does not reflect the choice Scottish voters facer at the general election on 12 December.
She said: "The SNP is the biggest party in Scotland, the third-biggest party at Westminster, we could hold the balance of power after this election.
"Our views should be heard, and indeed scrutinised, in this debate and it's deeply regrettable that won't happen."
Asked about Mr Johnson's comments that he would not debate her, Ms Sturgeon said: "He seems to be a big scaredy-cat.
"I remember when he came to Bute House in the summer and was getting into a debate about independence with me - privately I suggested to him then that we should take it to the public sphere and have a debate in public about that.
"He seemed to be up for that at the time, so I can't really throw any light on what has changed his mind."
Ms Sturgeon said it "spoke volumes" that Mr Johnson was only willing to go head-to-head with Mr Corbyn, adding: "I'll put down a challenge to him right now: I'll debate him any time, any place.
"So come on Boris, stop being so scared."
Ms Sturgeon was speaking during a campaign visit to a trampoline activity centre in Stirling, where she repeated her call for Scotland to be given more powers over immigration policy in order to help grow its economy.
As he arrived ahead of the debate, Mr Corbyn said he hoped it would be "respectful and informative", and that he would use it to outline how Labour's policies could "transform this country".
But the Liberal Democrats have said it is "outrageous that the Remain voice is missing" from the debate.
The BBC will also host a live head-to-head debate between the Conservative and Labour leaders in Southampton on 6 December, plus a seven-way podium debate between senior figures from the UK's major political parties on 29 November, live from Cardiff.
The Lib Dems have sent a legal letter to the BBC over its decision not to include Ms Swinson in the head-to-head.
BBC Scotland will stage a televised debate between the SNP, Conservatives, Labour and Liberal Democrats on 10 December, although the Scottish Greens have criticised the decision not to include them.