The British Prime Minister has arrived in Belfast tonight for his first visit to Northern Ireland.
Boris Johnson is to meet each of the five main political parties involved in talks aimed at reviving power-sharing at Stormont.
It is understood that he is meeting the DUP's Arlene Foster, Nigel Dodds and Jeffrey Donaldson tonight.
British PM @BorisJohnson has arrived in Northern Ireland, where he is this evening meeting DUP leader Arlene Foster, Nigel Dodds and Jeffrey Donaldson | https://t.co/9yw5ov48bj pic.twitter.com/JvVXdJcZKp— RTÉ News (@rtenews) July 30, 2019
Earlier today, Taoiseach, Leo Varadkar spoke by phone to the British Prime Minister - the first contact between the two leaders since Mr Johnson took over in Downing Street six days ago.
Mr Johnson told Mr Varadkar that his government will approach any negotiations that take place with determination and energy and in a spirit of friendship.
Following this morning's call, the Taoiseach's office issued a statement, saying that Mr Varadkar emphasised to Mr Johnson that the backstop was necessary as a consequence of the decisions taken by the UK and the EU is united in its view that the Withdrawal Agreement could not be opened.
He told the prime minister that alternative arrangements could replace the backstop in the future, but "thus far satisfactory options had yet to be identified and demonstrated".
The statement continued: "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 Taoiseach invited Mr Johnson to Dublin to "share further their respective analyses on Brexit and to continue discussion of bilateral matters including Northern Ireland, the Good Friday Agreement and the Common Travel Area".
Mr Johnson's spokeswoman said: "The Taoiseach congratulated the Prime Minister on his appointment and both leaders underscored their commitment to working closely together in the spirit of the warm and deep relationship between the UK and Ireland.
"On the process of restoring the Executive and Assembly in Northern Ireland, both leaders expressed their determination to see this happen as quickly as possible.
"The Prime Minister said the ongoing talks have his unequivocal support and that he wanted to continue to work closely with the Irish government to help drive the process towards a successful conclusion.
"He said he looked forward to visiting Northern Ireland shortly and talking to the leaders of the five main parties about this."
The spokeswoman added: "On Brexit, the Prime Minister made clear that the UK will be leaving the EU on October 31, no matter what.
"He said that in all scenarios, the government will be steadfast in its commitment to the Belfast Agreement and will never put physical checks or physical infrastructure on the border.
"The Prime Minister made clear that the government will approach any negotiations which take place with determination and energy and in a spirit of friendship, and that his clear preference is to leave the EU with a deal, but it must be one that abolishes the backstop.
"The two leaders agreed to stay in contact."
Clarification sought from Fianna Fáil on Brexit position
Elsewhere, Fianna Fáil leader Micheál Martin said on Twitter: "To be absolutely clear; the refusal by PM Boris Johnson to engage with European leaders and our Taoiseach without preconditions on the issue of Brexit is unacceptable and is not within the realms of normal diplomatic or political behaviour".
Mr Martin made the statement following strong criticism of his party TD, Timmy Dooley, who blamed the stand-off on what he described as a failure by the Taoiseach to "engage in basic diplomacy over the past two years."
In a tweet earlier, the Clare TD said: "The Government's lack of experience and arrogance will hurt Ireland in the coming months".
His comments drew sharp criticism from other parties who said he was trying to score political points at a sensitive time of Brexit negotiations and that they could be used against Ireland by British politicians.
Labour Party leader Brendan Howlin urged Mr Martin to clarify his party's position.
"I don't think for a minute that Micheál Martin wants to allow any divergence of view - any weakening of the solidarity that has been the strength of our negotiating position for the past two and a half years.
Speaking on RTÉ's News at One, he added: "If we are not unified on the backstop, it will comfort to those who want to tear us apart".
Fine Gael Senator Neale Richmond accused Fianna Fáil of trying to "undermine strong Irish consensus on Brexit."
This evening, the Independent Alliance called on all parties and Independents in the Oireachtas to support the Government position on Brexit.
Speaking on behalf of the group, Minister of State for Skills and Training, John Halligan, said support for the Government's position on Brexit should be united.
"This is a crucial time for our economy and political relationship with the UK. It is vitally important that the UK goes back to the Withdrawal Agreement it agreed with the EU.
"The only way forward is the Withdrawal Agreement. This policy has been agreed by all parties in the Dáil and it is vitally important that we all stay united on this on behalf of the people of Ireland," said Mr Halligan.
UK PM Johnson says now up to EU to compromise on Brexit
Speaking in Wales today, Mr Johnson said the next move in Brexit talks was up to the European Union, adding that he did not want to leave the bloc without a deal but had to prepare for that outcome just in case.
"If they can't compromise, if they really can't do it, then clearly we have to get ready for a no-deal exit," Mr Johnson said during a visit to Wales.
"It is up to the EU, this is their call, it's their call if they want us to do this."
Additional reporting PA