Sinn Féin assembly victory fuels debate on future of union

Leader Mary Lou McDonald raises issue of unification as nationalists become biggest party in Northern Ireland

Northern Ireland has slipped into political crisis after Sinn Fein's triumph in the assembly election triggered calls for a referendum on a united Ireland and the Democratic Unionist party vowed to block the formation of a new power-sharing executive at Stormont.

Jubilant Sinn Fein supporters celebrated across the region on Saturday when final vote counts confirmed a historic victory that turned the former IRA mouthpiece into the biggest party, with the right to nominate the first minister.