Plans to shred parts of the Northern Ireland protocol “would send headlines around the world” that the UK is prepared to break treaties, Ireland’s foreign minister has said, as a British cabinet minister insisted the UK did not intend to break the law.

The business secretary, Kwasi Kwarteng, said the UK had “the right to act in a sovereign way” and to “reopen or re-examine the protocol” but denied the actions would constitute a breach of international law.

Boris Johnson will travel to Belfast on Monday, where he will vow not to scrap the protocol negotiated as part of the Brexit deal, and say he is only seeking reform that has “the broadest possible cross-community support”.

In a move to put pressure back on parties at Stormont, Johnson will urge them to “get back to work” after the Democratic Unionists blocked the election of a Speaker at the Stormont assembly on Friday, meaning the assembly is unable to function.

Signs that the government was rowing back its rhetoric on the protocol came amid mixed messaging over a trade war, with Johnson allies claiming he had a “conciliatory” call with Ireland’s taoiseach last week. However, the Irish Times on Saturday reported Irish sources describing it as “the single worst call he has ever had with anyone”.

On Sunday, Simon Coveney, Ireland’s foreign minister, “criticised sabre-rattling and grandstanding” from ministers over the past week, including reported plans by the UK foreign secretary, Liz Truss, on Tuesday for a bill that would unilaterally override parts of the protocol in order to lift checks on goods crossing the Irish Sea.

Johnson has already been warned that dozens of Conservative MPs will attempt to stop the bill becoming law if it reaches the later stages – though many see it as a negotiating tactic.

Coveney told Sophy Ridge on Sky News on Sunday that the behaviour of UK ministers was “creating a lot of tension in my country, your closest neighbour, and also potentially being on the verge of making a decision that could fundamentally undermine the functioning of the institutions of the peace process in Northern Ireland”.

He said the majority of people in Northern Ireland were in favour of the protocol. “There is a minority, a large minority within unionism, who are unhappy with the protocol,” he said.

“There are solutions that we can put in place that can ease that concern and that’s what we need to focus on doing together, as opposed to the British government acting on its own, illegally in a way that doesn’t reflect majority opinion in Northern Ireland and perhaps, most importantly, sends a message to the world that this British government when it suits them will set aside international law.”

He said that the relations between Britain and Ireland were being fundamentally damaged because of “unhelpful briefings that we’re getting from very, very senior levels within the British government this week”.

Coveney said the EU had not threatened any specific retaliation – though several European parliamentarians have said there will be consequences, including the potential suspension of the trade deal, should the UK government act unilaterally.

“There’s no way the EU can compromise if the UK is threatening unilateral action to pass domestic legislation to set aside international obligations under an international treaty that, don’t forget, the UK was the primary designer of along with the EU,” he said.

“We can get there to a landing zone if we work in partnership. But, you know, sabre-rattling and grandstanding in Westminster ratcheting up tension is not the way to do it.”

Kwarteng said the UK had a right to act unilaterally contained within article 16 of the protocol – though sources close to Truss have briefed that invoking article 16 is not the route the government intends to take.

“Political stability in Northern Ireland is our number one priority,” Kwarteng told Ridge. “We should be able to act in a sovereign way. Northern Ireland is as much part of the United Kingdom as England, Cornwall, the south-east, and we are responsible for that.”

He said he did not think there would ultimately be a trade war with the EU and that any imposition of tariffs would be likely to take considerable time.

“I don’t think there is going to be a trade war. There has been a lot of talk, a lot of threats about what the EU will or won’t do. That is up to them,” he told the BBC’s Sunday Morning programme.

“As far as I am concerned, our primary duty as the British government is to look after political stability in Northern Ireland. If that means re-looking at the protocol, we absolutely have to do that.

“I think this talk of a trade war is irresponsible and I think it is completely getting ahead of ourselves. It is up to the EU. We think it would be completely self-defeating if they went into a trade war, but that is up to them.”