Boris Johnson has said it is up to the EU to compromise to avoid a no-deal Brexit, after his demands for the backstop to be scrapped were met with a flat refusal from the Irish taoiseach, Leo Varadkar.

In comments that showed he is preparing to blame the EU if the UK ends up leaving without a deal, Johnson said he was not aiming for a no-deal Brexit but the situation was “very much up to our friends and partners across the Channel”.

“They know that three times the House of Commons has thrown out that backstop, there’s no way that we can get it through, we have to have that backstop out of the deal, we cannot go on with the withdrawal agreement as it currently is,” he said.

“If they understand that then I think we are going to be at the races. If they can’t compromise, if they really can’t do it, then clearly we have to get ready for a no-deal exit.”

He said it was “up to the EU, this is their call if they want us to do this” but “unless we are determined to do it they won’t take us seriously in the course of the negotiations”.

Earlier, Johnson clashed with Varadkar in their first phone call since he entered Downing Street in which the taoiseach said the EU was united in the view that it cannot be scrapped.

Johnson finally spoke to Varadkar almost a week after becoming prime minister, telling him the UK would never put physical checks or infrastructure at the border with Northern Ireland after Brexit but demanding the backstop be scrapped.

The prime minister will travel to Northern Ireland on Wednesday with the overt aim of boosting progressing in the Stormont talks, meeting leaders from five of Northern Ireland’s political parties. His pre-briefed remarks made no reference to the border.

A spokesman for Varadkar said: “The taoiseach emphasised to the prime minister that the backstop was necessary as a consequence of decisions taken in the UK and by the UK government.

“Noting that the Brexit negotiations take place between the UK and the EU, the taoiseach explained that the EU was united in its view that the withdrawal agreement could not be reopened.

“Alternative arrangements could replace the backstop in the future, as envisaged in the withdrawal agreement and the political declaration on the future relationship, but thus far satisfactory options have yet to be identified and demonstrated.”

Quick guide What is the Brexit ‘backstop’? Show Hide What is the original ‘backstop’ in the withdrawal agreement? Variously described as an insurance policy or safety net, the backstop is a device in the withdrawal agreement intended to ensure that there will not be a hard border between Northern Ireland and the Republic of Ireland, even if no formal deal can be reached on trade and security arrangements. It would mean that if there were no workable agreement on such matters, Northern Ireland would stay in the customs union and much of the single market, guaranteeing a friction-free border with the Republic. This would keep the Good Friday agreement intact. Both the UK and EU signed up to the basic idea in December 2017 as part of the initial Brexit deal, but there have been disagreements since on how it would work. The DUP have objected to it, as it potentially treats Northern Ireland differently from the rest of the UK, creating a customs divide in the Irish Sea, which is anathema to the unionist party. Hardline Tory Eurosceptics also object to it, as they perceive it to be a trap that could potentially lock the UK into the EU’s customs union permanently if the UK & EU cannot seal a free trade agreement. That would prevent the UK from doing its own free trade deals with nations outside the bloc. What was added to May’s withdrawal agreement? Joint interpretative instrument

A legal add-on to the withdrawal agreement was given to Theresa May in January 2019 to try to get her deal through the UK parliament. It gives legal force to a letter from Jean-Claude Juncker and Donald Tusk, the presidents of the commission and council. This stated the EU’s intention to negotiate an alternative to the backstop so it would not be triggered, or, if it was triggered, to get out of it as quickly as possible. Unilateral statement from the UK This set out the British position that, if the backstop were to become permanent and talks on an alternative were going nowhere, the UK believes it would be able to exit the arrangement. Additional language in political declaration This emphasises the urgency felt on both sides to negotiate an alternative to the backstop, and flesh out what a technological fix would look like. However, it failed to persuade the attorney general, Geoffrey Cox, who said that while it ‘reduces the risk’ of the UK being trapped in a backstop indefinitely, it does not remove it. What happens next? Boris Johnson declared the Northern Ireland backstop ‘dead’ during his leadership campaign, and promised to throw it out of any deal he renegotiated with the EU. The EU has repeatedly stated that it will not reopen the withdrawal agreement for renegotiation. Daniel Boffey, Martin Belam and Peter Walker

An Irish government spokesman said Varadkar had also invited Johnson to Dublin for further talks on Brexit. “The taoiseach restated the need for both governments to be fully committed to the Good Friday agreement, the protection of the peace process and the restoration of the Northern Ireland institutions,” the spokesman said.

“He recalled that the agreement requires the sovereign government to exercise power with rigorous impartiality on behalf of all the people in full respect for their rights, equality, parity of esteem and just and equal treatment for the identity, ethos and aspirations of both communities.”

A No 10 spokesman said both leaders committed themselves to maintaining a warm and deep relationship between Ireland and the UK. But Johnson made clear his view the UK would be leaving the EU on 31 October regardless of whether a deal was struck and that any new agreement must be “one that abolishes the backstop”.

Johnson had been accused of snubbing his Irish counterpart by leaving it so long to speak to him, even though Varadkar will be central to whether he can agree a new withdrawal deal with the EU.

He has also drawn criticism for refusing to sit down for talks with EU leaders unless they agree there can be some movement on the Irish backstop. The leader of Ireland’s main opposition party, which is in a confidence and supply agreement with Leo Varadkar’s Fine Gael party, has said Johnson’s refusal to engage with Irish and other EU leaders is a breach of diplomatic protocol.

In a strongly worded statement put out on Twitter Micheál Martin said: “To be absolutely clear; the refusal by PM Boris Johnson to engage with European leaders and our taoiseach without pre conditions on the issue of Brexit is unacceptable and not within the realms of normal diplomatic or political behaviour.”

Varadkar has ruled out a deal without the backstop, which Eurosceptic Tory MPs refused to vote for because they argued it could indefinitely trap the UK in a customs union after the end of the transitional period.

Ireland regards the backstop as integral to preventing a return to a hard border with Northern Ireland if new customs arrangements have not been put in place by the time the UK leaves.

Johnson has not yet put forward a clear proposal for replacing the backstop but some senior Tory MPs believe the solution lies in “alternative arrangements”, whereby technology could be used to conduct customs checks away from the border.

In comments before the visit to Belfast, Johnson stressed that devolution needed to be restored as matter of urgency. “The people of Northern Ireland have now been without an executive and assembly for two years and six months – put simply this is much, much too long,” he said.

“Northern Ireland’s citizens need and deserve the executive to get up and running again as soon as possible, so that locally accountable politicians can take decisions on the issues that really matter to local people. I’m pleased to meet each of Northern Ireland’s party leaders today to stress that I am going to do everything in my power to make the ongoing talks to restore devolution a success.”

Julian Smith, the new Northern Ireland secretary, said the trip in the prime minister’s first full week underlined the importance of restoring the Northern Ireland executive to this new administration.

“It is of critical importance that new momentum is now introduced to the ongoing talks process, and that all of the parties work collectively to reach agreement,” he said. “I’m pleased the prime minister has agreed to meet each party and help drive the process forward.”