European Union's chief Brexit negotiator Michel Barnier gestures as he delivers a speech at the "Les Grandes Conferences Catholiques", in Brussels, Belgium, November 5, 2018. REUTERS/Francois Lenoir

BRATISLAVA (Reuters) - The European Union will not conclude an exit agreement with Britain or give London a transition period after Brexit without a deal that prevents a “hard” border in Ireland, the bloc’s main negotiator said on Tuesday.

Speaking at a joint news conference with Slovakia’s Prime Minister Peter Pellegrini, Michel Barnier said he would seek to agree the whole 100 percent of a draft Brexit accord with London.

“We are still not at the 100 percent,” Barnier said. “What is missing is a solution for the issue of Ireland.”

“Without an operational backstop there will not be an accord and there will not be a transition period. That is certain.”

Barnier said the EU was working to improve its offer for the so-called backstop, or an emergency fix to keep the Irish border open regardless of Brexit consequences, but that it must be workable, operational and all-weather.

“It cannot have an end-date. It must be applicable unless and until another solution is found,” he said.

The persistent differences over how to ensure maintaining an invisible Irish border have been the main hurdle to agreeing a Brexit deal in the unprecedented divorce negotiations to end more than four decades of Britain’s membership in the EU.

Uncertainty over whether the sides will be able to clinch a deal roiled sterling on Tuesday.

Barnier also said in separate comments to Belgian television RTBF that he was unable to declare at this stage that a deal was close.