A DUP MP has accused Dublin's government of acting "disgracefully" over the Irish border and he urged the UK to "shake their cage" in EU talks.
Ian Paisley said the UK should stop "pussy-footing around" if Dublin keeps on frustrating the will of UK citizens.
He urged Britain to make a fishing deal "long, tedious and hard" for Dublin, unless they acted in a "mature" way.
But Ireland's EU commissioner Phil Hogan said he expects to see "movement" on a border solution within days.
Speaking in Brussels on Wednesday, Mr Hogan said the UK had come "very close" to meeting the EU's terms on its so-called Brexit divorce bill, and he added that Britain would "hopefully" meet EU requirements on the Irish border.
"In the same way as we have seen movement in the last 24 hours in relation to the the financial settlement, I expect that we will see movement [on the Irish border] in the next few days as well, and hopefully we will," Mr Hogan said.
Earlier this month, Taoiseach (Irish prime minister) Leo Varadkar said Brexit trade talks should not proceed until the UK made a firm, written commitment to preventing a "hard" Irish border.
His ultimatum angered the Democratic Unionist Party and the party's MP for North Antrim, Ian Paisely, raised the issue in parliament during a meeting of the Northern Ireland Affairs committee.
"They (the Irish government) need to start acting in a mature way and deal with us as good neighbours and as friends instead of trying to frustrate the will of the people of the United Kingdom by saying they want a united Ireland; that they want this part of the sovereign territory of Her Majesty's Government to remain out with the rest of the agreements," Mr Paisley said.
"And I think that needs to be spelt out loud and clear, and if Her Majesty's Government isn't - for diplomat reasons - prepared to say it publicly, I hope that you're starting to shake their cage internally and privately in these negotiations."
Mr Paisley addressed his comments to Northern Ireland Office Minister Chloe Smith, but she made no direct response.
Earlier, Ms Smith told committee members that she could not share details of the government's contingency planning over Irish border issues because of "sensitivities" over the Stormont talks, which she said were ongoing.
This week, Sinn Féin said they saw no basis for becoming involved in further talks to restore Stormont at the moment.
Labour MP Conor McGinn asked Ms Smith if Sinn Féin's statement contradicted the government's position.
Meanwhile, the head of Northern Ireland's civil service has said planning for Brexit would be helped "considerably" if local ministers were in place.
Stormont has been without a devolved administration for almost a year.
David Sterling said it would be helpful to have ministers who could "advance Northern Ireland's cause with a single voice."
He said he was not making a political point.