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– Ireland's left-wing nationalist Sinn Fein party shattered the country's center-right status quo with its strongest-ever performance in this weekend's general election, throwing Irish politics into uncertainty.

Exit polls and early vote counts showed Sinn Fein on par with or ahead of the two mainstream parties that have dominated Irish politics for nearly a century, with young voters embracing the long-marginalized party en masse.

The center-right Fine Gael party of Prime Minister Leo Varadkar suffered humiliating losses. In an embarrassing turn of events, Varadkar was outperformed by the left-wing nationalists in his own constituency, though he is expected to keep his seat under Irish electoral rules.

"This is no longer a two-party system," said Mary Lou McDonald, leader of Sinn Fein, the former political wing of the Irish Republican Army.

Vote counting continued throughout Sunday, but no party appeared to have an easy path to forming a majority government. A second election could be needed if no breakthrough is reached.

McDonald indicated that she would first seek to form a government with smaller parties. Meanwhile, the leader of the center-right Fianna Fail party, Micheál Martin, said there is "an obligation on all" to ensure the formation of a functioning government.

Martin did not explicitly address the key question, however, of whether such a government could include Sinn Fein.

Ahead of the election, Martin and Fine Gael leader Varadkar had both insisted they were not inclined to govern with the left-wing nationalists.

For the two center-right parties, Sinn Fein's historical association with the IRA still weighs heavily. The IRA, loyalist paramilitaries and British troops killed about 3,600 people during the conflict known as the Troubles, which centered on the IRA's campaign to force an end to British rule in Northern Ireland from the 1960s until the late 1990s. It continues to haunt Irish politics, especially as Britain's recent departure from the European Union has raised new concerns that Irish peace could be at risk.

Brexit played a minor role in Ireland's Saturday election, following a campaign that was largely dominated by housing and health care. McDonald appeared to capitalize on voters' frustration with the country's two center-right parties and increasing support for left-wing economic policies.

Brought up in a middle-class Dublin suburb, McDonald, 50, framed herself as a progressive, urban leader in an effort to move the party on from its controversial roots.