Belfast (Reuters) - Northern Ireland’s largest nationalist party on Tuesday called on the Irish government to prepare for the unification of the British region with EU-member Ireland, saying “bullish” Boris Johnson’s Brexit posed a threat.

FILE PHOTO: Sinn Fein Leader Mary Lou McDonald leaves a meeting with European Union Chief Brexit Negotiator Michel Barnier at the EU Commission headquarters in Brussels, Belgium April 1, 2019. REUTERS/Francois Lenoir

Sinn Fein leader Mary Lou McDonald told supporters in Belfast that Johnson was “not my prime minister”.

Her comments come days after Irish Prime Minister Leo Varadkar said the question of the unification of Ireland and British-ruled Northern Ireland would inevitably arise if Britain leaves the European Union without a divorce deal on Oct. 31.

Johnson, who succeeded Theresa May as Britain’s prime minister last week, has vowed to take Britain out of the EU “no ifs or buts” on Oct. 31, deal or no deal.

“In the week since a jingoistic and bullish Boris Johnson strode into Downing Street and appointed a staunchly Brexiteer cabinet,” there has been speculation about what it means for the people of Northern Ireland, McDonald said.

“Elements of our political establishment tell us that now is not the time to discuss Irish unity. They are wrong. Now is exactly the right time to discuss it,” she said.

“The government has to begin planning for unity.”

When Britain voted to leave the European Union, few voters outside Northern Ireland cited the fate of the British region.

But the possibility of a disorderly EU exit has encouraged those who want another referendum - on the reunification of Northern Ireland and Ireland.

While overall Britons voted 52% to 48% to leave the EU in the 2016 referendum, 56 percent of people in Northern Ireland voted to remain.

“The route back for the north into the EU is clear, Irish unity is the route back to the EU,” McDonald said.

More than 3,600 people died in three decades of violence between Irish nationalists, who want a united Ireland, and the British security forces and pro-British “unionists” defending the region’s British status.

The 1998 Good Friday Agreement, which ended the violence, foresees the holding of referendums on both sides of the border on uniting the island, if London and Dublin see public support for that. The British government has said it does not believe there is sufficient support now.

McDonald said she would raise the issue of Irish unification at a meeting with Johnson in Belfast later this week.

The Sinn Fein leader also said interparty talks being held in Belfast in a bid to restore the power-sharing local administration, which collapsed two and a half years ago, were not making progress.