WEIMAR, Germany — The German, French and Polish foreign ministers have vowed to increase ties between their countries when Britain leaves the EU to secure a safer and more effective union.

"Confronted by unparallelled challenges in Europe... (we must) intensify cooperation and create a new drive," Frank-Walter Steinmeier, Jean-Marc Ayrault and Witold Waszczykowski said in a joint statement on Sunday.

They were gathered in the eastern German town of Weimar to celebrate the 25th anniversary of the "Weimar Triangle" political forum.

They vowed to "reinforce the foundations of European integration... aspiring to a more flexible EU that reflects the different ambitions of member states regarding increased integration" once Britain had left the bloc.

Talks between the 27 EU nations remaining in the bloc are likely to be challenging, as Berlin’s preferred vision of a centralised, federal Europe clashes with proposals for a confederation of nation states popular among leaders of eastern EU members.

The three foreign ministers gathered in Weimar also called for the bloc’s combined foreign and security policies to be strengthened with the creation of an annual European Security Council meeting of EU heads of government.

Their comments came as German Chancellor Angela Merkel said on Sunday that the refusal of some EU countries to accept Muslim refugees is "unacceptable" and called for quotas to divide the influx throughout the bloc.

"We know that there is no simple answer to these challenges, but we are determined to confront them together in a spirit of renewed mutual confidence," said the ministers’ statement.

The Weimar Triangle, created in 1991, is a consultative body that promotes cooperation and common interests between the three EU states. — AFP