Large parts of the Polish population during the Holocaust believed that helping Jews went against their local norms, a new study from the Polish Academy of Sciences shows.

The academy, a state-run institution, focused on a period beginning in 1942 that saw an intense effort on the part of the Nazi occupiers to wipe out Jewish ghettos across Poland.

The study compares the fates of Jews who managed to escape the ghettos during that period and reveals that those who tried to seek shelter in urban areas were less likely to survive, compared to Jews who escaped to the country, who had a much better chance of staying alive.

According to the scholars, this can be explained by the norms that were prevalent among Poles in urban areas.

“Poles who chose to save Jews were essentially violating the unwritten norms of their community,” the scholars wrote.

The new publication comes amid renewed tension between Israel and Poland over the issue of Polish complicity in Nazi atrocities during the Holocaust.

On Sunday, newly appointed acting Foreign Minister Yisrael Katz drew anger when he quoted former Prime Minister Yitzhak Shamir, who said that Poles “suckle anti-Semitism with their mothers’ milk,” resulting in a diplomatic crisis between the two countries.

Shamir’s parents and two sisters died during the  Holocaust. Shamir claimed that his father was killed just outside his birthplace in Ruzhany by villagers who had been his childhood friends, after he had escaped from a German train transporting Jews to the death camps.

The acting minister made the accusation in reference to a controversial Polish law that makes it a civil offense to accuse the Polish nation, rather than individual Poles, of complicity in the Holocaust.