Taoiseach Leo Varadkar has said there will be no further EU concessions to help the British government win the support of the DUP for the new Brexit deal.
e also said the Government was "disappointed" that the House of Commons had not yet voted on the deal struck between British Prime Minister Boris Johnson and the EU.
He said yesterday that a Brexit extension was preferable to a crash-out Brexit "if it comes to it".
The DUP is opposing the deal as it is against the prospect of a de facto customs border down the Irish Sea. Mr Varadkar ruled out further concessions aimed at getting the DUP onside.
"This is done now - we have negotiated two deals with the UK government at this stage, both of them supported by 28 governments," he said.
"There isn't going to be any further changes and I think the UK government acknowledges that.
"Obviously the Government is disappointed that there wasn't a vote in the House of Commons on the Brexit deal at the weekend.
"The UK has now requested an extension and, of course, an extension would be preferable to no deal if it comes to it."
Mr Varadkar cautioned that an extension would need the unanimity of the 27 member states.
He said member states "are reasonably asking what is the purpose of this extension".
"Is it more time to ratify the deal, or is it for something else?" he asked.
"And I think some clarity from Westminster on that would be very helpful."
Mr Varadkar said he believed the risk of no deal was "relatively low".
"Nonetheless, we need to continue to prepare for it and as a result of that, we are not stepping down our plans of preparing for a no deal," the Taoiseach added.
He said that there were "quite a number of MPs" in Westminster who voted for an extension, adding: "A lot of them have indicated they will vote for the deal.
"So, I think it is more likely than unlikely that a deal will eventually pass."
European Council President Donald Tusk is expected to spend the coming days canvassing opinions among EU leaders on their views on the British request for an extension. Mr Varadkar is expected to be on Mr Tusk's call sheet.
Sources last night said this would take place at the same time as the "fluid environment" in the House of Commons.
Meanwhile, the DUP's Sammy Wilson has said his party was not backing a second Brexit referendum.
The DUP supported the Letwin amendment, two days after it rejected Mr Johnson's new Brexit deal. The amendment says Westminster will withhold approval of the deal until the withdrawal bill implementing Brexit has been passed.
Mr Wilson said his party's votes "were significant" in the passing of the amendment.
"DUP MPs supported the Letwin amendment as the only avenue available to properly scrutinise the deal on offer and attempt to secure changes that could address some of the concerns we have," he said.
He moved to quash any suggestions the DUP would support a second referendum.
"The DUP does not seek a second referendum, merely implementation of the first," he said.
"The people of the United Kingdom were asked whether the UK should leave the EU, not whether Great Britain should leave Northern Ireland behind.
"We want to leave as one nation. That remains our goal.
"If the prime minister remains willing to achieve that outcome, he will find DUP MPs as willing partners in that project."