Poland and Greece still eye WWII billions from Germany

"A group of experts is dealing with this in the Polish parliament. MPs will debate it and decide on the next steps," he said.

"Warsaw was levelled to the ground. The experts' initial results show that we were never compensated for this," he added.

The German newspaper cited previous comments by Poland's ruling Law and Justice (PiS) party to say the Polish claim could total €690bn.

The Polish reparations process comes amid similar developments in Greece, where a report by cross-party MPs has said Germany owed Athens €299bn for damages caused by its Nazi-era occupation of the country.

"This is an issue that psychologically still rankles, and as a government we are absolutely determined to raise it," an MP from the ruling Syriza party, Costas Douzinas, told British newspaper The Guardian.

"Obviously Greece couldn't do that [claim reparations] when it was in a [bailout] programme receiving loans from the EU and Berlin. It would have been totally contradictory," the MP, who also teaches law in the UK, added.

"Germany has never properly assumed its historical responsibility for the wholesale destruction of the country," Stelios Koulouglou, a Syriza MEP in Brussels, also said.

Nazi occupation "played a major part in delaying our country's development as a modern European state," he added.

The Polish comments came despite a show of friendship between Berlin and Warsaw.

Duda met German president Frank-Walter Steinmeier in Germany last week, while Polish and German government ministers will hold talks in Poland this week.

Duda, in Bild am Sonntag, also praised the fact no major German party had ever questioned its WWII guilt and said he admired the cleanliness of German homes and towns.

Unity in doubt

But the reparation claims would test European unity still further at a time when Poland is already being seen as a difficult member state over its government meddling in the judiciary and its opposition to migrant-sharing.

Duda defended Polish plans to force Supreme Court judges into early retirement on grounds that the older ones among them had been stooges of its former communist regime.

The "democratic institutions of member states should play a deciding role" in the EU, he added, after the European Commission took the Polish government to task in the judicial dispute.

Duda, while in Berlin last week, said Brexit was caused by EU interference in domestic affairs, such as an EU ban on energy-wasting lightbulbs.

But Jaroslaw Kaczynski, the powerful PiS party chief, adopted a less populist tone at a party congress in Radom, in central Poland, also on Sunday.

Change of tone

"We know we must respect European law and we will respect it," he said, referring to an EU court injunction to halt the forced judicial retirements.

The idea that PiS wanted Poland to quit the EU was an opposition lie designed to harm its reputation in recent local elections, he added.

"The idea that PiS is preparing a 'Polexit' is a lie, a lie, and, once again, a lie," Kaczynski said.

Poland wanted to model itself on Ireland in the way it spent EU funds and in the way that its ruling and opposition parties worked together on the European stage, he added.

"If we want Poland to advance, we must model ourselves on those who achieved success. Ireland is such a country," the right-wing politician said.