The DUP has said the Irish backstop remains its "key problem" with the Brexit agreement reached between British Prime Minister Theresa May and the European Union.
The party held talks with government ministers in London today, as Prime Minister Theresa May seeks to build support for her deal after it suffered a fresh setback.
Support from the DUP could lead to the agreement being approved by the House of Commons next week, after it was defeated for the second time on Tuesday.
Speaking after the talks, DUP deputy leader Nigel Dodds said the discussions were "constructive" and would continue "over the coming period of time".
Mr Dodds said: "At the end of the day, some of the concerns we have been raising are not new.
"For us the key problem with the Withdrawal Agreement is the Irish backstop.
"From day one, our focus has been on the red line of how Northern Ireland is treated separately from the rest of the UK.
"But I think what is new now is there is a renewed focus in government on ensuring those issues are addressed."
Mr Dodds said that extra cash for Northern Ireland did not form part of the discussions.
The talks come as European leaders consider whether to agree to UK calls for its departure to be delayed.
MPs backed a delay to Brexit beyond the scheduled departure date of 29 March in dramatic parliamentary scenes which saw a majority of the Conservative party in the opposite lobby from the Prime Minister.
But any delay will require the agreement of the other 27 European Union members, with talks about any conditions for an extension set to begin before leaders gather at a summit next week.
European Council President Donald Tusk met Dutch Prime Minister Mark Rutte in The Hague today before talks with the bloc's key power brokers Angela Merkel and Emmanuel Macron on Monday.
On Tuesday, Mr Tusk will travel to Dublin to meet Taoiseach Leo Varadkar before the summit in Brussels on Thursday.
Mr Tusk said: "I will appeal to the EU27 to be open to a long extension if the UK finds it necessary to rethink its Brexit strategy and build consensus around it."
Tánaiste Simon Coveney has described the next few days as "crucial" for the UK to secure an extension to Article 50.
Mr Coveney said that EU leaders want a clear idea of the purpose of an extension to the Brexit process before granting a delay.
He was speaking after a meeting in France with its Minister for Europe Nathalie Loiseau.
EP Brexit coordinator questions Article 50 extension
European Parliament Brexit coordinator Guy Verhofstadt has questioned why the leaders of the 27 should grant an extension if Mrs May was "not ready for a cross-party approach to break the current deadlock" in the Commons.
Mrs May is set to bring her Brexit deal back to the Commons for a third meaningful vote next week, and Attorney General Geoffrey Cox has sought to provide further legal assurances about the Irish backstop.
But Mrs May's hopes of persuading Eurosceptics and the DUP to back the deal were dealt a blow after the "Star Chamber" of Brexiteer lawyers rejected Mr Cox's latest assessment.
The group of lawyers, led by veteran Tory Bill Cash, said a suggestion that the UK could use the Vienna Convention - the international agreement that lays down the rules about treaties - to unilaterally pull out of the backstop was "badly misconceived".
The panel of lawyers, which significantly also includes DUP deputy leader Nigel Dodds, rejected the supplementary legal advice from Mr Cox.
The Attorney General's advice hinges on Article 62 of the Vienna Convention, which says that if there has been "a fundamental change of circumstances" following the conclusion of a treaty "which was not foreseen by the parties", then the countries involved would be allowed to withdraw from it.
Mr Cox said: "It is in my view clear and undoubted in those exceptional circumstances that international law provides the (UK) with the right to terminate the Withdrawal Agreement."
But the Brexit-backing lawyers said "given the high burden that a state must meet to use it, and given the extreme reluctance of international courts and tribunals to accept it" the Vienna Convention route "supplies no assurance whatsoever that the UK could terminate the Withdrawal Agreement in a lawful manner".
Downing Street sources denied that Mrs May had lost control of her Cabinet or her party, insisting that the results were a "natural consequence" of the decision to offer a free vote on an issue where many hold strong views.
The motion authorising the prime minister to request an extension to the two-year Article 50 negotiation process, was passed by 413 votes to 202 - a majority of 211.
Only a refusal by the leaders of the 27 remaining EU states to grant the UK an extension at a Brussels summit next week could now preserve the totemic date of 29 March as Brexit Day.
Mrs May has made clear that she hopes to bring her Agreement back to the Commons by 20 March in the hope of securing the support of MPs who rejected it by 230 votes in January and 149 earlier this week.
If she succeeds, she will go to the Brussels summit to request a short delay to a date no later than 30 June, to give herself time to pass legislative changes necessary for a smooth and orderly Brexit.
But if her deal is rejected for a third time, she believes any extension would have to be far longer and would involve the UK taking part in European Parliament elections in May.
Mr Varadkar said: "I think we need to be open to any request they make, listen attentively and be generous in our response."
A spokesman for the European Commission said President Jean-Claude Juncker was "in constant contact with all leaders".