Secretary of State for Northern Ireland Chris Heaton-Harris has said there will be no renegotiation of the UK/EU deal to address issues linked to the Northern Ireland Protocol.
Mr Heaton-Harris was speaking after meeting the five main parties at Hillsborough Castle near Belfast.
He said the so-called Windsor Framework, announced last month, would not be reopened for further talks.
"That deal is done and that deal is going to be accepted at a joint committee meeting tomorrow and will become international law shortly afterwards," he told reporters.
"There is no renegotiating of that deal and we're now going to put our best efforts into making that deal work - that's both us and the European Union."
His intervention turns the screw on the DUP which says it's holding out for further concessions before it will agree to restore powersharing at Stormont.
And the prospect of a challenging Stormont budget, which in the absence of an Executive will have to be set by Mr Heaton-Harris, will pile on more pressure.
It will create public pressure to get back into government to sort out huge challenges in health and other public services.
Mr Heaton-Harris said he believed the DUP had not fully grasped the import of yesterday's Westminster vote which overwhelming endorsed a key element of the Windsor Framework.
The so-called Stormont Brake will give MLAs a role in deciding what new EU laws apply in Northern Ireland.
The DUP says the British government oversold it as some kind of veto.
Mr Heaton-Harris spoke of the nature of his talks with Northern Ireland party leaders at Hillsborough.
"We've been talking about the Windsor Framework, how a deal that everybody said that could not be done between the UK Government and the European Union has been done to solve all the practical and many other issues that were caused by the Northern Ireland Protocol of the past, and that that deal is done," he said.
"And that deal is going to be accepted at a joint committee meeting tomorrow and will become international law shortly afterwards. There is no renegotiating of that deal."
Taoiseach 'disappointed' with DUP's rejection
Earlier, Taoiseach Leo Varadkar said he is disappointed that the DUP has chosen not to return to Stormont following yesterday's House of Commons vote.
He told reporters in Brussels: "I'm disappointed to hear that the DUP isn't willing to go back into the executive and assembly. I think they should.
"People in Northern Ireland are facing big problems, inflation, a housing crisis, a health service that's under enormous pressure, all the problems that we face, and worse.
"What they need is their politicians in Stormont in government, sorting out those problems for them."
Mr Varadkar is in Brussels today for a meeting of European Union leaders where the framework will be discussed.
DUP 'not interested in sticking plasters' over issues
Mr Donaldson said he is 'not interested in a sticking plasters' to the problems besetting powersharing in Northern Ireland.
He was speaking after meeting Mr Heaton-Harris.
"I want Northern Ireland to work. I am not interested in sticking plasters," Mr Donaldson said.
"They don't work. And I'm afraid in the Windsor Framework, there is an element of the sticking plaster and it won't work.
"It will not deliver the long-term stability and prosperity that Northern Ireland needs."
Sinn Féin leader Mary Lou McDonald said the time for prevarication over the return of the Stormont was over.
She said a forthcoming budget for Northern Ireland to be set by Mr Heaton-Harris would be hugely challenging for all communities in Northern Ireland.
"The damage that will be done by having no Executive and no Government will be felt on a cross-community basis," Ms McDonald said.
Mr Heaton-Harris said the Windsor Framework is "not a sticking plaster, it's a solution to the problems that were produced by the protocol and it will work".
"And the two sides to those negotiations which have concluded, the UK government and the European Union, are going to make the framework work," he said.
"So there is nothing more to get out of that conversation. It is done.
"Now I think it's down to the communities of Northern Ireland to work out how best it can work for them. I think it can work for them really well."
Additional reporting: Conor Macauley and Tony Connelly