Poland and Israel have used full-page ads in German newspapers, including the conservative daily Frankfurter Allgemeine Zeitung, to praise their countries' ties and comment on Poland's controversial Holocaust law.

The "joint declaration" begins by stating that "for 30 years, relations between our countries and peoples have been built on a solid foundation of trust and understanding," and goes on to say both nations are united by a "deep, long-lasting friendship" marked by "mutual respect for the identity and historical sensitivity of our tragic past." The ad was published in the name of Israeli Prime Minister Benjamin Netanyahu and his Polish counterpart Mateusz Morawiecki.

Poland's divisive Holocaust law

The ad signals a warming of ties after tension had arisen between both countries over Poland's controversial Holocaust law. Passed in early 2018, the law instantly drew condemnation from Israel, the United States and Ukraine.

It stipulated fines and jail sentences of up to three years for individuals who "publicly and in denial of the facts" blame Poles or the Polish state for carrying full or partial responsibility for crimes committed by Nazi Germany.

Read more: Auschwitz: Evolution of a death camp and Holocaust memorial

Critics feared the law would prevent Holocaust survivors and historians from researching the role that some Poles played in Germany's genocide against the Jews.

Relations between Poland and Israel were so fraught that Netanyahu accused Poland of trying to rewrite history and possibly even deny the Holocaust.

Six months later, at Morawiecki's behest, Poland revised the law and cut any reference to possible jail sentences.

Why publish in the German press?

That Poland and Israel would buy such an ad in the German press may, at first glance, appear surprising. But it isn't really, according to Manuel Sarrazin, a member of Germany's Green party who chairs the German-Polish parliament group.

"It is important for Germany that Poland and Israel are on good terms," he said, adding that the ad indicates both sides have resumed friendly relations.

He welcomed efforts from Poland and Israel to intensify their dialogue over their shared history.

"In Germany, we need to realize that Poland's domestic debate [regarding the Holocaust] is also partly due to German media, which failed to distance itself from its own, revisionist portrayals of history," he said. German media has occasionally mistakenly referred to Nazi concentration camps in occupied Poland as "Polish death camps."

The Polish-Israeli ad states that it is "clear the Holocaust represents an unprecedented crime committed by Nazi Germany against the Jews and all Poles of Jewish descent" and adds that Poland "has always shown it fully understands the significance of the Holocaust."

But the ad also concedes: "We recognize that there were horrific acts committed by Poles against Jews during World War II, and we condemn every one of these."

At the same time, the ad highlights the "heroic actions of many Poles," who risked their own lives to save Jews.