Theresa May has told Jeremy Corbyn it is "impossible" for the government to rule out a no-deal Brexit as he has demanded.
The Prime Minister was responding to the Labour leader after he snubbed talks offered by Mrs May over the terms of her Brexit deal - and tried to ban his MPs from doing the same.
Mr Corbyn said he would only enter negotiations when Mrs May takes no-deal "off the table".
But Mrs May, in a letter to her rival, said this is an "impossible condition" because it is not within the government's power to do it.
She said: "I note that you have said that 'ruling out' no deal is a precondition before we can meet, but that is an impossible condition because it is not within the government's power to rule out no deal.
"Let me explain why. Under Article 50 of the Treaty on European Union and the Withdrawal Act 2018, we will leave the EU without a deal on 29 March unless Parliament either agrees a deal with the EU or the UK revokes article 50 and chooses to stay in the EU permanently.
"So there are two way to avoid no deal: either vote for a deal, in particular a Withdrawal Agreement, that has been agreed with the EU, or to revoke Article 50 and overturn the referendum result.
"I believe it would be wrong to overturn the referendum result."
Mr Corbyn has urged Labour MPs not to "engage" with the government over its Brexit deal after at least three prominent backbenchers took up an offer of talks with ministers.
The Labour leader sent a letter to members of the parliamentary party after Hilary Benn, Yvette Cooper and John Mann all visited the Cabinet Office for talks in Whitehall on Thursday.
Their visits came just hours after Mr Corbyn had used a speech in Hastings to reiterate his demand that a no-deal Brexit must be ruled out before he would take up Theresa May's offer of talks.
In his subsequent letter to MPs, Mr Corbyn said no deal would be "disastrous" and must be off the table, adding: "I urge colleagues to respect that condition and refrain from engagement with the government until 'no deal' is taken off the table."
Both Mr Benn - who said he wanted to see if there was an "open mind" behind the offer of talks as he went in - and Ms Cooper had echoed Mr Corbyn's demands on no deal as they left the Cabinet office later on Thursday afternoon.
Mr Corbyn wrote to Prime Minister Theresa May - who offered cross-party talks on Wednesday after surviving the Labour leader's motion of no confidence - demanding she removes the threat of no deal before they meet.
Additional reporting by Press Association.
