Northern Ireland's Democratic Unionist Party accused Britain on Tuesday of keeping it in the dark over a proposed Brexit deal on the Irish border but said it would examine the text after blocking an agreement in Brussels.

"The text only came through to us late yesterday morning. Obviously once we saw the text, we knew that it was not going to be acceptable," DUP leader Arlene Foster told Irish public broadcaster RTE.

"Now we need to look at the text, make it clear what we cannot agree with and try to work through all of that because we want to move to phase two as much as anybody else," Foster said, referring to the next stage of UK-EU talks on a future trade partnership.

Foster, whose support in parliament keeps British Prime Minister Theresa May's Conservative government in office, was due to speak with the premier later Tuesday.

European Commission president Jean-Claude Juncker said he would then be meeting May "in the course of this week", either on Wednesday, Thursday or Sunday.

London had reportedly agreed that Northern Ireland, part of the UK, would maintain "regulatory alignment" with EU-member Ireland after Brexit, even as the UK as a whole withdraws from the bloc's single market and customs union.

Dublin had demanded guarantees that Brexit would not lead to the return of frontier checks, which could incite sectarian tensions in a region once plagued by violence.

But as May sought to close the deal over lunch with Juncker in Brussels on Monday, the DUP, Northern Ireland's pro-British biggest party, made clear its opposition.

Foster said that the draft agreement was a "big shock" and she accused the Irish government of pursuing an "aggressive agenda" of Irish reunification.

She also said she had been told by British negotiators that the Irish government had prevented them from sending a draft text to the DUP.

- Left behind? -

Several Conservative MPs have also expressed alarm, with one leading Brexit supporter, Jacob Rees-Mogg, warning "the government doesn't have a majority" to effectively move the EU customs border into the Irish Sea.

Source: AFP