Boris Johnson has refused to say whether he will take part in a BBC interview with presenter Andrew Neil.
The leaders of Labour, the SNP, the Lib Dems and the Brexit Party have all agreed to be questioned for 30 minutes by the journalist.
But when asked several times by the BBC's Ben Wright if he would appear, the prime minister would not confirm it, saying he would have "all sorts of interviews with all sorts of people".
Labour accused him of "running scared".
On Wednesday, the BBC Press Office tweeted it was "in ongoing discussions" with No 10, but said they had not "yet been able to fix a date" for the sit-down discussion between Mr Neil and the PM.
Conservative leader Mr Johnson - who faced Andrew Neil during the Conservative leadership election in July - confirmed negotiations were still taking place, but he said it was "not my job" to make the final decision.
He added: "Other people than me are responsible for those discussions and negotiations, and I do not want to pre-empt what they may decide."
When it was put to Mr Johnson that his critics would say he was avoiding scrutiny, he replied: "I'm very happy to submit to all manner of scrutiny, all manner of debates and have done so, and lots of conversations are happening about that matter right now."
The BBC's interview with Lib Dem leader Jo Swinson is set to air on 4 December and another with Brexit Party leader Nigel Farage will be shown on 5 December.
Labour Party chairman Ian Lavery said of Mr Johnson: "He's running scared because every time he is confronted with the impact of nine years of austerity, the-cost-of-living crisis and over his plans to sell out our NHS, the more he is exposed."
In a separate row, Channel 4 News has criticised Mr Johnson and Brexit Party leader Nigel Farage for declining invitations to take part in a debate about climate change.
The hour-long Emergency On Planet Earth debate features Labour leader Jeremy Corbyn, Liberal Democrat leader Jo Swinson, Scottish First Minister and SNP leader Nicola Sturgeon, Plaid Cymru's leader Adam Price and Green co-leader Sian Berry.
The Conservatives offered cabinet minister Michael Gove instead of Mr Johnson - but Mr Gove was turned away from the Channel 4 News studios ahead of the debate.
Channel 4 News editor Ben de Pear tweeted that Mr Gove and Boris Johnson's father Stanley, who accompanied him, were "lovely and charming but neither are the leader".
The broadcaster set up two ice sculptures alongside empty podiums, representing the absence of Mr Johnson and Nigel Farage.
Mr de Pear said: "These two ice sculptures represent the emergency on planet earth, not in any human form but are a visual metaphor for the Conservative and Brexit parties after their leaders declined our repeated invitations to attend tonight's vital climate debate."
And at the end of the debate, Channel 4 presenter Krishnan Guru-Murthy said: "As we made clear from the start, this debate was for leaders only.
"And our leaders were only prepared to debate other leaders."
Speaking in a Facebook Live video on the Conservative Party's page, Mr Gove claimed the other party leaders "vetoed" him from appearing on the programme.
He said: "I wanted to take part, but unfortunately [when] the editor of Channel 4 News... asked the other party leaders, they all said 'absolutely no'.
"They'd rather debate a block of ice."
The Conservative Party has written to broadcasting regulator Ofcom accusing Channel 4 of breaking its codes by depriving the Tories of any representation at the debate.
The party calls the "empty chairing" of Mr Johnson - and his replacement with an ice sculpture - a "provocative partisan stunt, which would itself constitute making a political opinion in its own right," something the Tory letter argues is against the broadcasting code.
"It is clear that denying the Conservative Party any opportunity to contribute to this cross-party event is unfair and breaches the requirements to 'preserve' impartiality and does not offer an 'appropriately wide range of significant views' to the public," the letter adds.
It comes after a Conservative source told BuzzFeed News that if the party wins the coming election it will reassess Channel 4's public service broadcasting licence, after Mr Johnson was replaced by the ice sculpture.
In response to the BuzzFeed story, Labour's deputy leader Tom Watson said it was "deeply concerning" for Mr Johnson to "threaten Channel 4 in this way".
Labour says Mr Watson has written to Ofcom to urge the regulator to "call out this meddling".
The Liberal Democrat's shadow foreign secretary Chuka Umunna said the alleged threat to Channel 4 was a "pathetic attempt to cover up for Boris Johnson's own cowardice", adding: "Time and again Johnson has tried to duck scrutiny."
A live TV election debate featuring representatives from seven political parties takes place on BBC One and the BBC News Channel on Friday at 19:00 GMT.
Senior figures from the Conservatives, Labour, Lib Dems, SNP, Greens, Plaid Cymru and the Brexit Party will take part in the event, chaired by Nick Robinson, in Cardiff.
Follow Ben Wright @BBCBenWright
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