LONDON — The European Union said Wednesday that "difficult" talks with Britain have failed to break the Brexit deadlock, as the UK chief law officer claimed the two sides were holding "robust" discussions on new British proposals.

As Britain lurches toward an EU exit due in just over three weeks, EU Commission spokesman Margaritis Schinas said that "while the talks take place in a constructive atmosphere, discussions have been difficult."

"No solution has been identified at this point," he said.

Attorney General Geoffrey Cox said a meeting Tuesday with EU chief negotiator Michel Barnier had been "robust" — often a code-word for fraught with disagreement.

"These are very sensitive discussions. We're into the meat of the matter now," Cox told Sky News. "We have put forward some proposals — very reasonable proposals — and we're now really into the detail of the discussions."

Britain is due to leave the bloc on March 29. But the UK Parliament has so far rejected a divorce deal laying out the terms of an orderly departure and a transition period for businesses to adjust to new trade rules.

British concerns center on a provision designed to keep an open border between the UK's Northern Ireland and EU member Ireland. The mechanism, known as the backstop, is a safeguard that would keep the UK in a customs union with the other 27 EU countries in order to remove the need for checks until a permanent new trading relationship is in place.

Brexit-supporting lawmakers in the UK fear the backstop could be used to bind Britain to EU regulations indefinitely, and Prime Minister Theresa May wants to revise the deal to reassure opponents that it would only apply temporarily.

EU leaders insist that the legally binding Brexit withdrawal agreement can't be reopened, and talks are focusing on drafting an addendum or other additional words.

May has said she will bring the deal back to Parliament — with any changes she has secured — by Tuesday. If it is rejected again, lawmakers will vote on whether to leave the EU without an agreement or seek to delay Brexit.

UK businesses overwhelmingly oppose a "no-deal" exit, which would impose tariffs and other barriers between Britain and the EU, its biggest trading partner. It could also destabilize Northern Ireland's peace process, which has come to rely on free movement of people and goods across an open border.

Northern Ireland civil service chief David Sterling warned that "there is currently no mitigation available for the severe consequences of a no-deal outcome," including a sharp increase in unemployment and an exodus of businesses to the Republic of Ireland.

"The consequences of material business failure as a result of a 'no-deal' exit, combined with changes to everyday life and potential border frictions could well have a profound and long-lasting impact on society," Sterling said in a letter to Northern Ireland political leaders.

Sammy Wilson, a lawmaker for Northern Ireland's Democratic Unionist Party, accused Sterling of having "a political motive" and called his letter "a scare tactic."

The Protestant Unionist DUP is strongly opposed to the backstop, saying it will force checks between Northern Ireland and the rest of the UK The party's 10 lawmakers prop up May's minority government in the House of Commons.

"I don't care if he's head of the civil service or Santa Claus, it really doesn't matter, the fact of the matter is, he's got it wrong," Wilson said.

AP