Brussels is ready to give the UK further "guarantees, assurances and clarifications" that the Irish backstop should only be temporary, Michel Barnier has said.
The EU's chief Brexit negotiator insisted that the controversial measure, intended to avoid a hard border on Ireland, will not be removed from the Withdrawal Agreement.
While acknowledging Brexiteer concerns that the backstop is a trap that would keep the UK tied to the EU indefinitely, Mr Barnier insisted it is only "insurance" intended for the "worst-case scenario".
Speaking to German newspaper Die Welt, Mr Barnier said: "We know that there are misgivings in Britain that the backstop could keep Britain forever connected to the EU.
"This is not the case. And we are ready to give further guarantees, assurances and clarifications that the backstop should only be temporary."
The guarantees in question could come as an adjunct to the withdrawal agreement in the form of an "interpretive document".
However the EU will not allow for a time limit to be placed on the backstop or give Britain the right to unilaterally pull out of it, Mr Barnier said.
The development came as the president of Slovenia suggested the country and many other EU states would be willing to accept a short delay to Brexit.
Borut Pahor, who sat on the European Council of leaders when he was prime minister, told Sky News: "I think Slovenia and a lot of other countries would say yes.
"I think that nobody wants to see a hard Brexit in a chaotic way, which would damage London and Brussels and Ljubljana and every country."
However Mr Pahor said the extension should not be used simply to postpone the making of a compromise decision.
Prime Minister Theresa May gave into pressure from pro-Europe ministers this week by offering MPs the chance to vote to seek an extension to Article 50 to delay EU departure on March 29 if her deal is defeated and a no-deal Brexit is rejected.
Meanwhile Jeremy Corbyn confirmed Labour would now back a referendum if faced with a "damaging Tory Brexit" or a no-deal departure from the European Union after Labour's vision was rejected in the Commons.
Chief Secretary to the Treasury Liz Truss warned on Friday that a new Brexit referendum would provoke a "massive crisis".
She also indicated that a no-deal exit could be better than a delay.
Ms Truss told the BBC: "I think it would be an absolute disaster if we had a second referendum after people voted so clearly to leave the European Union.
"There will be a massive crisis in this nation. And it would be terrible for business. It would leave us continuing in this limbo period."