It will be “very difficult” for the UK and the EU to reach a Brexit agreement before the 31 October deadline, Irish leader Leo Varadkar has said.
He told Irish broadcaster RTE “big gaps” remained between the two sides.
Amid claims on Tuesday that talks were close to collapse, he also suggested the language around the discussions had turned toxic “in some quarters”.
Mr Varadkar and Boris Johnson are expected to meet for further Brexit talks later this week.
The UK has said the EU needs to “move quickly” to stop it leaving without an agreement at the end of the month.
Taoiseach Leo Varadkar, who spoke with Mr Johnson by phone for about 45 minutes on Tuesday, said he would strive until the “last moment” to reach a deal with the UK, but “not at any cost” to his country, Northern Ireland and the rest of Europe.
He also downplayed the chances of any agreement being struck before the crucial summit of EU leaders on 17 October, during which next steps for Brexit are likely to be decided.
“I think it’s going to be very difficult to secure an agreement by next week, quite frankly,” Mr Varadkar said.
“Essentially, what the UK has done is repudiated the deal that we negotiated in good faith with prime minister [Theresa] May’s government over two years and have sort of put half of that now back on the table, and are saying that’s a concession. And of course it isn’t really.”
Mr Varadkar added that it was his job to hold the UK to commitments it had made since the 2016 referendum to prevent a hard border on the island of Ireland and uphold the Good Friday Agreement.
The Irish leader’s comments came after a No 10 source claimed on Tuesday that Germany was now making it “essentially impossible” for the UK to leave the EU with a deal.
That assessment followed a “frank” phone call between Boris Johnson and German Chancellor Angela Merkel, during which they discussed Brexit proposals the UK prime minister put forward last week to the EU.
After the call, a No 10 source said Mrs Merkel had made clear a deal based on the prime minister’s plans was “overwhelmingly unlikely” – though the BBC’s Adam Fleming said there was “scepticism” within the EU that she would have used such language.
The No 10 source also suggested Mrs Merkel told her counterpart the only way to break the deadlock was for Northern Ireland to stay in the customs union and for it to permanently accept EU single market rules on trade in goods.
This, the source said, marked a shift in Germany’s approach and made a negotiated deal “essentially impossible”.
In response, the EU’s top official, European Council President Donald Tusk, accused Mr Johnson of engaging in a “stupid blame game”.
In a tweet to the prime minister, he added: “At stake is the future of Europe and the UK, as well as the security and interests of our people.
“You don’t want a deal, you don’t want an extension, you don’t want to revoke, quo vadis (where are you going)?”
European Commission president Jean-Claude Juncker said that if negotiations fail, “the explanation will be found in the British camp (because) the original sin is found on the islands and not on the continent”.
Speaking to the French Les Echos newspaper, he added: “A no-deal Brexit would lead to a collapse of the United Kingdom and a weakening of growth on the continent.”
In his interview with RTE, Mr Varadkar was asked whether he was concerned the language around the talks was “getting toxic”.
“I think it is, from some quarters, but you know I don’t play dirty. You know, I don’t think most EU leaders do either. We’ve been very straight up from when the referendum happened.”
The prime minister also hosted European Parliament president David Sassoli in Downing Street on Tuesday, but the MEP left saying “no progress” had been made.
Mr Sassoli later told the BBC’s Newsnight programme: “Angela Merkel’s opinions must be taken seriously. We are all very worried because there are only a few days left.
“Because we understand that going out without an agreement leads to having a real problem, if not a real catastrophe.”
Following the meeting, Downing Street said there was “little time” left to negotiate a new legally-binding withdrawal agreement, but Mr Johnson remained committed to doing all he could.
“We need to move quickly and work together to agree a deal,” a No 10 spokesman said.
“He [the prime minister] reiterated that if we did not reach an agreement then the UK will leave without a deal on 31 October.”
The PM’s pledge comes despite legislation passed by MPs last month, known as the Benn Act, which requires Mr Johnson to write to the EU requesting a further delay if no deal is signed off by Parliament by 19 October – unless MPs agree to a no-deal Brexit.
While negotiations are continuing in Brussels, Mr Sassoli said a deal likely to command the support of MEPs was a “long way off”.
Meanwhile, 19 Labour MPs have written to the European Commission president Mr Junker calling for a Brexit deal to be made with the government without any further delay.
Caroline Flint, who represents the leave-supporting constituency of Don Valley, told BBC Radio 4’s Today programme the “uncertainty of Brexit has gone on too long” and the group did not think it was “impossible” to resolve the Irish border issue.
Timeline: What’s happening ahead of Brexit deadline?
Tuesday 8 October – The House of Commons was prorogued – suspended – ahead of a Queen’s Speech to begin a new parliamentary session.
Monday 14 October – The Commons is due to return, and the government will use the Queen’s Speech to set out its legislative agenda. The speech will then be debated by MPs throughout the week.
Thursday 17 October – Crucial two-day summit of EU leaders begins in Brussels. This is the last such meeting currently scheduled before the Brexit deadline.
Saturday 19 October – Date by which the PM must ask the EU for another delay to Brexit under the Benn Act, if no Brexit deal has been approved by Parliament and they have not agreed to the UK leaving with no-deal.
Thursday 31 October – Date by which the UK is due to leave the EU, with or without a withdrawal agreement.