Boris Johnson has said the Government will not accept a Northern Ireland-only backstop.
The compromise plan was first offered by the EU at an early stage in negotiations with Theresa May .
But it was dropped after the hardline DUP, who propped up the Tory Government, responded angrily.
Answering a question on the current state of the backstop during the session of People’s PMQs , Mr Johnson said: “The backstop is going to be removed … I very much hope, or I insist.”
The Prime Minister added: “Without that, there is not going to be a deal.”
Earlier today the Prime Minister held talks with the Conservatives’ key parliamentary allies the DUP, with leader Arlene Foster and her deputy Nigel Dodds spending more than an hour inside Downing Street.
Mr Johnson continued: “We will not accept a Northern Ireland-only backstop. We have to solve the problem of the Northern Ireland border but we’re working very hard to do that.”
DUP leader Arlene Foster has said her party was working with Mr Johnson to find a deal that sees Northern Ireland leave the EU with the rest of the UK.
Ms Foster said a Northern Ireland-only backstop would mean one part of the UK would be left in the customs union and subject to the rules of the single market without any consent.
Mrs Foster said the Prime Minister demonstrated his “commitment to securing a deal which works for the entire United Kingdom” as well as the Republic of Ireland, including rejecting the idea of a Northern Ireland-only backstop – which would have created a special economic zone for the country.
Some have suggested that since Mr Johnson has already lost his majority the Northern Irish MPs are less important.
The idea of a Northern Ireland-only backstop, which could build on a common food and agricultural zone across Ireland, is popular in the province.
Mr Johnson fuelled speculation he could extend this to effectively create a border down the Irish Sea at a press conference in Dublin.
“The landing zone is clear. We need to find a way to ensure the UK is not kept locked in the backstop arrangement and there’s a way out for the UK,” he said.
“Strip away the politics and at the core of each problem you find practical issues that can be resolved with sufficient energy and a spirit of compromise.
Tory sources suggested he might be prepared to consider a Northern Ireland only backstop in a bid to reach agreement with Brussels.
Sinn Fein president Mary Lou McDonald has said UK Prime Minister Boris Johnson is following a Brexit “fantasy”, and that his plan is “profoundly stupid and immeasurably dangerous”.
Speaking at her party’s away day in Dundalk, Co Louth, Ms McDonald said: “British Prime Minister Boris Johnson follows a fantasy in which the rights and interests of the Irish people can be cast aside.
“It is time to call Mr Johnson’s fantasy for what it is – profoundly stupid and immeasurably dangerous.”
She added: “Mr Johnson’s stupid, dangerous fantasy cannot become Ireland’s nightmare, because Brexit is a very English problem and the consequences of it cannot be shifted on to Ireland.”
Ms McDonald also said Ireland faces “its greatest threat and challenge in a generation”.
“As October 31 approaches, neither an Taoiseach (Leo Varadkar) or (EU chief Brexit negotiator) Michel Barnier can blink in the face of Tory intransigence, because too much is at stake,” she said.
Ms McDonald said Mr Johnson’s Brexit plan would lead to a hard border on the island of Ireland.
She said: “Despite Mr Johnson’s claims to the contrary, the path he is leading would lead us to a hard border. The British Prime Minister needs to hear this.
“The Irish people will not allow our country, our communities, our economy or our peace to be vandalised by him.
“There can be no return to a hard border, customs checks, and no more division on this island to suit the needs of a British Government that has no interest in Ireland’s future.”
But Ms McDonald said “no viable alternative exists to the backstop”.
“It is not perfect by any means but it’s the least worst option and broad Irish opinion supports that,” she said.
“This isn’t about us stamping our feet, this is a compromise solution, a minimum insurance policy.
“I believe that despite DUP rhetoric to the contrary, broad Irish opinion north and south understands that and supports that.
“If the DUP were representing northern citizens and society well they would recognise that. They are very much adrift from the consensus position in the north and the south.”
Ms McDonald added that preparations must now be made for a united Ireland and that her party will run on an abstentionist ticket.
“No true Irish republican would ever take a seat in the British Parliament, much less swear an oath to the British crown,” she said.