BELFAST - UK Prime Minister Boris Johnson steps into an increasingly bitter row on Monday when he visits Northern Ireland to urge the formation of a power-sharing executive, which is currently being blocked by a Brexit dispute.

In a historic development, the role of Northern Ireland’s first minister is set to be taken by the pro-Irish party Sinn Fein, after it triumphed in elections to the Stormont assembly earlier this month.

But the pro-UK Democratic Unionist Party (DUP), angered at the “Northern Ireland Protocol” agreed as part of Britain’s Brexit deal with the European Union, blocked the election of a speaker at Stormont.

Johnson will meet all parties involved and is expected to tell them that London will “play its part to ensure political stability”, but that Northern Ireland politicians must “get back to work” to deal with “bread-and-butter issues”, according to a statement from his office Sunday.

The DUP is refusing to help form an executive until the protocol is changed to get rid of trade checks between Northern Ireland and mainland Great Britain, which it believes are threatening the province’s status within the UK.

Johnson’s government also insists the protocol is threatening the delicate balance of peace in Northern Ireland between the pro-Irish nationalist community and those in favour of continued union with the UK.

It has warned it will trigger Article 16 of the Brexit deal to suspend the agreement, or legislate to eliminate its requirements from UK law, unless the EU agrees to change it.

Writing in Monday’s Belfast Telegraph, Johnson said that those who wanted to scrap the protocol were “focusing on the wrong thing”.

“I hope the EU’s position changes,” Johnson wrote. “If it does not, there will be a necessity to act.”

“We will set out a more detailed assessment and next steps to parliament in the coming days, once I return from discussions with the local parties.”

In London, Johnson’s spokesman told journalists that Foreign Secretary Liz Truss would speak in parliament on Tuesday “to set out the rationale for our approach”.

Irish foreign minister Simon Coveney warned London against taking unilateral action.

“Northern Ireland is about compromise and trying to find middle-ground positions that everybody can live with, to maintain political stability,” Coveney told journalists in Brussels.

“That’s the approach we need to take at the moment, not a unilateral action or threats of unilateral action, which I think is deeply unhelpful.”

“To act unilaterally to break international law, to not respect the democratic decisions in Northern Ireland would make matters significantly worse, not better, in terms of trying to solve the problems of the protocol,” Coveney said.

“That is the last thing Europe needs right now when we’re working so well together in the face of Russian aggression and responding to the support needed for Ukraine at this time.”

Sinn Fein’s Northern Ireland leader Michelle O’Neill accused the DUP of holding the British-ruled territory to “ransom”.

“I intend to put it to him (Johnson) directly that he needs to stop pandering to the DUP,” she told reporters last week.

The UK government was “playing a game of chicken with the (European) commission right now, and we’re caught in the middle”, the first minister-elect added.

The protocol mandates checks on goods coming to the province from England, Scotland and Wales, to ensure no return of a physical border between Northern Ireland and EU member Ireland to the south.

The elimination of the hard border was a key strand of the 1998 Good Friday Agreement, which ended three decades of sectarian violence in Northern Ireland.

Johnson’s visit is expected to coincide with a delegation from the US Congress. The United States was a guarantor of the Good Friday Agreement, and has expressed alarm at the UK’s threats over the protocol.