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KILCOOLE, Ireland (Reuters) - Northern Ireland’s 1998 peace deal will need to be amended in the wake of Britain’s vote to leave the European Union as it contains references to the bloc, former British prime minister Tony Blair said on Friday.

Blair helped oversee the agreement between Irish nationalists and pro-British unionists, which brought an end to three decades of bloodshed that killed 3,600 people, in one of the biggest achievements of his 10 years in power.

“The Good Friday or Belfast Agreement was formulated on the assumption that both countries were part of the EU ... Some of the language will therefore require amendment because of Brexit,” Blair told a gathering of center-right European People’s Party, the biggest faction in the European parliament, according to comments published on his web site.

“With goodwill, including from our European partners, this should be achievable with the minimum of difficulty,” he said.

Blair called on the gathered politicians to do everything possible to avoid the creation of a “hard border” with physical border posts, which he said would be a disaster for Northern Ireland’s economy and fragile politics.

Irish Prime Minister Enda Kenny has said any semblance of a return to physical infrastructure along the border that was marked by military checkpoints until 1998 could lead to a renewal of the armed conflict.

While Brussels and London agree on the goal of avoiding a hard border, they have yet to clearly explain how the currently invisible border can be maintained after Brexit.