Germany's Foreign Minister Heiko Maas on Monday rejected an idea floated by his Polish counterpart to put a five-year limit on the Irish border "backstop" in any Brexit deal with Britain.

Ireland's Foreign Minister Simon Coveney had swiftly rejected the Polish proposal earlier on Monday.

"I am completely with my Irish colleague. He has already said what he thinks of it, which is nothing," Maas told journalists after talks in Brussels.

Maas urged unity among the 27 countries staying in the European Union. The bloc awaits new ideas from London, after the British parliament struck down the Brexit deal Prime Minister Theresa May had negotiated with the EU.