European Council President Donald Tusk has warned that there can't be progress toward a post-Brexit trade deal until the issue of the Irish border is resolved.
Tusk says that until Britain presents a plan to keep the all-but-invisible border open, "it is very difficult to imagine substantive progress in Brexit negotiations."
Britain and the EU agreed in December that there must be no customs posts or other impediments along the border between Northern Ireland and EU member Ireland. But they have not agreed on how to do it.
Britain has rejected the EU's suggestion, which is to keep Northern Ireland inside the bloc's customs union.
Speaking Thursday alongside Irish Prime Minister Leo Varadkar in Dublin, Tusk said Britain must propose "a specific and realistic solution to avoid a hard border."