BELFAST (Reuters) - Northern Ireland’s main political parties will resume talks on Monday to break a deadlock that threatens devolved government, the cornerstone of peace in the province for almost two decades, the British government said.

The Stormont Parliament building, where the Northern Ireland Assembly sits, is seen in Belfast, Northern Ireland March 3, 2017. REUTERS/Toby Melville

A political crisis has gripped Northern Ireland since Irish nationalist party Sinn Fein pulled out of government in January, which sparked a March 2 election that ended the majority pro-British unionists had enjoyed for almost a century.

No one is predicting the political impasse might pitch Northern Ireland back into the violence between Catholic nationalists and Protestant unionists that killed 3,600 people in three decades before a 1998 peace deal.

But the impasse may increase sectarian tensions and freeze decision-making as Britain prepares to leave the European Union. The last time devolved government collapsed, it took five years to reinstate it.

This week, nationalists and unionists missed a deadline to form a coalition government after three weeks of talks that one party described as a “shambles”.

But the British government has said it will not start to revert powers to London until April 18, giving the parties an additional two weeks to strike a deal.

After criticism from all sides about the format of the talks, the parties are to agree an agenda and hold structured, bilateral and roundtable meetings overseen by the British and Irish governments, the London said in a statement.

The talks will also explicitly address “the implementation of outstanding issues from previous agreements”, it said.

Sinn Fein argues that previous deals to give legal status to the Irish language and to proceed with inquiries into deaths during the decades of sectarian violence have not been honored.

Their main rivals, the Democratic Unionist Party, have accused Sinn Fein - which has long sought Northern Ireland’s merger with the Irish Republic - of demanding too many concessions because they want the talks to fail.