BRUSSELS (AP) — A top European Union official says Britain and the EU could yet fail to reach an agreement on the terms of their divorce, just six months before the U.K. is due to leave the bloc.

EU Council President Donald Tusk wrote Tuesday that "unfortunately, a no deal scenario is still quite possible. But if we all act responsibly, we can avoid a catastrophe."

His warning came in an invitation letter to EU leaders for a summit in Salzburg, Austria, starting Wednesday evening.

Tusk, who will chair the meeting, wants the 27 leaders — minus Prime Minister Theresa May — to reach agreement on the terms of a text outlining their future relations with Britain after it leaves next March.