Minister of State for European Affairs Helen McEntee has said the UK must live up to its obligations to prevent the return of a hard border and protect the peace process.
Ms McEntee told BBC Radio 4's Today programme: "We absolutely expect that the UK will fulfil its commitment, and will live up to its obligations because Brexit, or no Brexit, the UK Government is a co-guarantor of what is an international peace treaty.
"And integral to protecting that peace treaty is ensuring that we never return to any kind of borders that we saw in the past."
Ms McEntee insisted a backstop to prevent a hard border was "absolutely necessary", saying: "There seems to be a discussion ongoing at the moment that we will tweak, or we'll amend, or we might take out the Irish backstop.
"We are not at the beginning of negotiations. This is not a question as to whether or not we need an Irish backstop.
"Brexit happened more than two-and-a-half years ago, negotiations have been ongoing for two years and it is because of the UK's red lines, it is because the UK has said we are leaving the single market, we are leaving the customs union, and for us that makes it more difficult to avoid a border.
"It is because of those red lines that a backstop is absolutely necessary."
Ms McEntee said: "I think now, for some reason, the onus by the UK has been shifted back on Ireland. That we should compromise. That we are the ones that are trying to be awkward or difficult.
"We did not vote for Brexit. We do not believe in it. We absolutely respect that it was a democratic decision, of course we do.
"We are protecting a peace process. There is an obligation on the UK to ensure that the peace process, the Good Friday Agreement, is protected.
"And any suggestion that they can walk away from that, we simply won't accept that."
She added: "For us the Good Friday Agreement is much more important than Brexit."