The EU says no solution has been found to date to address the Brexit backstop impasse.
It comes a day after the latest high-level talks between British ministers and the EU's chief negotiator Michel Barnier.
The British government has been trying to seek changes to the Irish backstop, the insurance policy to avoid a hard border in Ireland after Brexit.
However, European Commission spokesperson Margaritis Schinas today said the talks have been "difficult".
In a press conference, he explained: "Michel Barnier, our chief negotiator... informed the commissioners that while the talks take place in a constructive atmosphere, discussions have been difficult.
"No solution has been identified at this point which is consistent with the withdrawal agreement, including the protocol on Ireland and Northern Ireland, which you all know will not be reopened."
Both the UK's attorney general Geoffrey Cox and Brexit secretary Stephen Barclay were in Brussels yesterday for the latest round of negotiations.
Ahead of the meeting, Mr Barclay insisted they were "determined to get a deal over the line and deliver on Brexit".
Theresa May's withdrawal agreement has previously been rejected by MPs, who've instead called for the government to seek 'alternative arrangements' to address the backstop.
MPs in Westminster are due to have their next 'meaningful vote' on the agreement and any changes to it next week.
If it's rejected again, they'll be asked whether they support leaving the EU without a deal.
If that's also voted down, politicians will vote on a possible short delay to Brexit to allow for further negotiations with the EU.
However, any extension to Article 50 will need to be agreed by European leaders.
The EU's currently scheduled to leave the bloc on March 29th - only three weeks from Friday.
Yesterday, Tánaiste Simon Coveney said it was his understanding that Brexit negotiations in Brussels "have been difficult".
In comments published over the weekend, Mr Barnier again warned that the backstop would not be reversed.
He said the EU was ready to give “further guarantees, assurances and clarifications that the backstop should only be temporary".