Sinn Fein Leader Mary Lou McDonald arrives for a meeting with European Union Chief Brexit Negotiator Michel Barnier at the EU Commission headquarters in Brussels, Belgium July 23, 2018. REUTERS/Francois Lenoir/File Photo

(Reuters) - The leader of the Irish Republican party, Sinn Fein, said on Tuesday that a Brexit withdrawal agreement must provide legal backing to the Irish prime minister’s guarantee that there should be no hard border with the British province of Northern Ireland.

“Last December, a joint report by UK and EU negotiators was agreed, in which it was stated there would be no hard border in Ireland,” Mary Lou McDonald said. “The Taoiseach (Irish prime minister Leo Varadkar) assured us that this was a ‘cast iron’ guarantee”.