British Prime Minister Theresa May has said political uncertainty in Northern Ireland must not be allowed to affect a peace process that has largely ended decades of sectarian violence in the province.

Northern Ireland's deputy leader, Martin McGuinness, resigned on Monday, effectively collapsing its devolved government and risking political paralysis in the region as Britain plans its exit from the EU.

McGuinness is a Nationalist, whose Sinn Fein party wants Northern Ireland to be united with the Republic of Ireland.

Under power-sharing rules, the province's first minister and McGuinness' coalition partner, Arlene Foster, must go too. She is a Democratic Unionist and wants Northern Ireland to remain part of the UK.

Restoring the power balance will be tough, with the potential to inflame old tensions. The power vacuum means that for the first time in 20 years the British government is back in direct control.

"The progress that has been made in Northern Ireland has been hard-won and we must all recognise that we don't want to put that progress in jeopardy," May told parliament on Wednesday.

McGuinness said he resigned in protest over his power-sharing partner's botched handling of a green energy scheme that left a big hole in the government's finances.

But the divisions between the two parties go much deeper.

For 30 years, Catholic Nationalists and Protestant Unionists fought for control of Northern Ireland with the British army heavily involved in the violence.

A peace deal was reached 19 years ago but old rivalries continued.

Elections inevitable

In West Belfast, Catholic communities have seen funds for Irish language projects cut. An example, they say, of a system that still favours the Unionists.

"This is a catastrophic financial situation that we're facing, but it's entirely based upon an arrogance and contempt shown by political Unionism," Declan Kearney, Sinn Fein's chairman, told Al Jazeera.

"We're now saying that that status quo has degraded the basis of our political institutions and we're determined to end this."

But Unionists say McGuinness' resignation was motivated by divisions within the Republican camp. He is also said to be suffering from a serious heart problem.

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"We're disappointed with his departure because it doesn't really solve the problems that are facing Northern Ireland," Peter Weir, a member of the Democratic Unionist Party, told Al Jazeera.

"It's clearly something that's been driven by internal Republican dissent but the problem is that the people of Northern Ireland are becoming the victims of that internal debate."

An investigation into the energy scandal has been ordered. But it is too late to save the government, and analysts say elections are now almost inevitable.