BELFAST (Reuters) - Northern Ireland could be set for a fresh election or a return to direct British rule of the province after the two main parties in negotiations to form a new government said on Sunday that talks had run their course without success.

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The British province’s nationalist and unionist parties have until Monday to form a new power-sharing government after snap elections this month or risk decision-making being taken back to London for the first time since 2007.

Sinn Fein, the province’s largest nationalist party, said that no substantive progress had been made on any of the key issues responsible for the impasse and that it would not support nominations to form a new regional executive.

“This talks process has run its course,” the party’s Northern Ireland leader Michelle O’Neill told reporters.

Both O’Neill and the leader of the main pro-British party, the Democratic Unionist Party’s (DUP) Arlene Foster, blamed each other for the collapse, with Foster saying there was little to suggest that Sinn Fein wanted to secure agreement.

“While regrettable, the reality is that sufficient progress was not achieved in the time available to form a new executive,” Foster said in a statement.

Sinn Fein had collapsed the previous government and surged to within one seat of the DUP at the March 2 election to deny pro-British unionist politicians a majority in the regional assembly for the first time since Ireland was partitioned in 1921.

Britain’s Northern Ireland minister James Brokenshire responded by urging the parties “even at this stage” to agree to work to form an executive, a position backed by Irish foreign minister Charlie Flanagan.

“This is a critical time for Northern Ireland. We are on the cusp on the triggering of Article 50 by the British Government,” Flanagan said referring to Britain’s plans to begin the process of the leaving the European Union this week.

Northern Ireland is considered the region of the United Kingdom most economically exposed to Brexit because of its close trade links to the Republic of Ireland. The border between the two is the UK’s only land border with the EU.

If there is no agreement by Monday’s 1500 GMT deadline, Brokenshire will have to decide whether to call another election -- the third in less than a year -- or to legislate for a return to direct British rule of the province, something he has repeatedly said he is against.

Irish Prime Minister Enda Kenny has raised the prospect that the parties could be given more time to form a new devolved administration, but Britain’s government has not proposed an extension and Sinn Fein is against such a move.