UK Prime Minister is playing games with Ireland and using it as a pawn in the country's ongoing trade battle with the European Union following the Brexit deal, Sinn Fein leader Mary Lou McDonald said Sunday before Johnson makes it to Northern Ireland on Monday.

Johnson will visit Belfast on Monday for talks after the pro-UK unionist Democratic Unionist Party (DPU) blocked the election of a speaker in the Stormont assembly, the Northern Ireland Assembly, just a week after the Sinn Fein emerged victorious following a game-changing election.

The British PM's talks will take place with politicians in Northern Ireland, but McDonald accused the premier of being in "cahoots" with the pro-London party stopping an executive and assembly sitting.

The Stormont by-laws stipulate that a new administration only be formed without the largest unionist party taking part.

"He has connived with the DUP to use Ireland, the north of Ireland, to use unionism in Ireland as a pawn in a wider game that is being played out with the European Union," McDonald said in reference to Johnson.

She went on to call his tactic and approach "shameful" and "absolutely not acceptable".

"It is very clear that the Tory government in London is in cahoots with the DUP to stall and to hold back progress, to frustrate the will of the people as expressed in the election, and that, to anybody who calls themselves a democrat, is clearly unacceptable and clearly shameful. And that case will be made to Boris Johnson," she stressed.

Following the latest election, the DUP became Northern Ireland's second-largest party, losing the seat it had kept since the formation of Northern Ireland in 1921.

The unionist party is opposed to the protocol as it means checks on goods passing between Britain and Northern Ireland while allowing the border between the North and the Republic to stay open in line with the Good Friday agreement.

Sinn Fein, an Irish nationalist party in Northern Ireland, celebrated a historic first-ever win in elections for Nothern Ireland, prompting the pro-UK unionists to threaten a government boycott when a cabinet is elected.

Sinn Fein has been fighting for a referendum to reunify Ireland with Northern Ireland after the north was created as a Protestant territory. Sinn Fein eyes 28 seats to gain the seat of first minister for Sinn Fein leader Michelle O'Neill.

The win came after the leader of North Ireland's Democratic Unionist Party (DUP), Jeffrey Donaldson, warned against a referendum on Irish unity, calling such legislation "divisive".

The DUP lost three seats in the election, and its refusal to cooperate with the Sinn Fein in Northern Ireland, prompting the Sinn Fein's leader in Northern Ireland, Michelle O'Neill. The party suffered the defeat due to several issues, mainly the resignation of the first minister, Paul Givan, in February.