German troops march through the Polish mud to the front lines on September 13, 1939 | Hulton Archive/Getty Images Poland could seek war reparations from Germany, say parliament researchers Berlin rejects the claim, which could sour relations between the two EU countries.

WARSAW — Poland can demand reparations from Germany for the damage and loss of life it suffered during World War II, according to a report by the Polish parliament's research service published Monday.

"It is legitimate to claim that the Republic of Poland is entitled to compensation claims against the Federal Republic of Germany, and the contention that those claims have expired is unfounded," the parliament's research bureau found in a 40-page opinion delving into the enormous devastation and millions of deaths that followed Germany's invasion of Poland on September 1, 1939.

Poland's ruling Law and Justice party (PiS) revived the reparations issue over the summer, reopening a matter that had lain dormant for years. It threatens to sour Warsaw's relations with Berlin at a time when Poland is exchanging insults with France and facing action from the European Commission over charges that it is violating the EU's democratic standards and refusing to accept asylum seekers.

The research bureau's opinion says Poland suffered material damage of $48.8 billion in 1939 dollars, equivalent to about $860 billion today. The document also underlines that over six million Polish citizens were killed during the war.

The analysis was requested by Law and Justice MP Arkadiusz Mularczyk.

"This is the first such complex analysis of the reparations issue, which has only been taken up in a very piecemeal way so far," Mularczyk told POLITICO. "It's clear that Poland did not receive due reparations. What it did receive was not even 1 percent of what Germany paid to other countries."

The Polish foreign ministry tweeted that more thorough analysis is needed before the government can decide whether to pursue Germany for damages.

Berlin has ruled out paying reparations to Poland, pointing out that Warsaw gave up its reparations claims in 1953. After joining the EU in 2004, the democratic Polish government confirmed the position adopted by its communist predecessor.

“From our point of view, that conclusively resolves the question — legally as well as politically,” German government spokesman Steffen Seibert said on Friday in Berlin, adding that no compensation demand has been made by the Polish government.

However, the parliamentary report argues that the 1953 decision was taken by a puppet government under Moscow's control in violation of the Polish constitution of the time.

The document acknowledges that Germany paid nearly 732 million Polish zloty (€173 million) to about 1 million Poles. It goes on to say, however, that other countries received more and the German reparations policy toward Poland was “discriminatory.”

Jarosław Kaczyński, the PiS leader and Poland's de facto ruler, has made the appeal for compensation a powerful part of his party's political appeal — the idea is supported by 63 percent of Poles, according to a recent survey.

"Poland never gave up these reparations, and those who claim otherwise are wrong," Kaczyński told a party gathering over the summer.

Poland's opposition parties have been careful not to rule out reparations, but warned that any clumsy attempt to demand them could open up a host of problems for Poland.

Tomasz Siemoniak, deputy leader of the opposition Civic Platform party and a former defense minister, told reporters that while Poland does have the right to seek compensation, the current effort is a "propaganda game" that will worsen relations with Germany and end up helping Russia.

The biggest worry over reopening the issue of the war is that it could also cast doubt on Poland's current borders. After the war, the Soviet Union annexed parts of prewar eastern Poland, and in return Poland was given large areas of Germany.

“Raising the question of reparations could lead to undermining international treaties with Germany under which we have a stable western border,” history professor Andrzej Friszke told the Rzeczpospolita newspaper.