A far-right Polish lawmaker displayed a paper Israeli flag emblazoned with a swastika in parliament, accusing the country of "genocide" in the Middle East, with Israel slamming his actions as "antisemitic horror".
"Israel is in the process of committing a genocide of exceptional cruelty before our very eyes," Konrad Berkowicz told lawmakers, comparing the country to a "new Third Reich".
Berkowicz, a member of the far-right nationalist Konfederacja (Confederation) opposition party, then brandished the paper flag, with the Nazi symbol replacing the Star of David at its center.
Parliamentarians reacted with outrage in a country that was the site of many of the concentration camps built by Nazi Germany during the Holocaust, in which six million European Jews were killed.
Berkowicz's actions prompted shouts of anger in the chamber, while the parliament speaker called the display of the swastika "unjustified".
The speaker later announced he was preparing a motion to impose penalties on Berkowicz for "presenting Nazi symbols in the chamber".
The Israeli embassy in Poland condemned Berkowicz's actions, calling them an "antisemitic horror" and demanding Polish authorities "act upon this disgrace".
The incident came on the same day the annual "March of the Living," held on the grounds of the former Nazi death camp Auschwitz commemorating Holocaust victims, took place.
Auschwitz was the largest of the extermination camps built by Nazi Germany in occupied Poland and has become a symbol of the Holocaust.
"As Holocaust Survivors march in Auschwitz today, this vile anti-Jewish act is especially appalling," the Israeli embassy wrote in a statement on X.
Berkowicz also accused the Israeli army of using white phosphorous bombs in the Middle East, describing in detail the severe injuries, suffering, and deaths of "tens of thousands of women and children" by such weapons.
Human Rights Watch has accused Israel of "illegally" using white phosphorous in Southern Lebanon after launching an offensive against Hezbollah.
Israel has said it "could not confirm" the allegations.
Berkowicz's actions prompted an immediate reaction from the United States ambassador to Poland, himself a follower of Orthodox Judaism.
"SHAME SHAME SHAME on YOU!! Maybe even you have noticed that we Jews aren't so easy to push around anymore, are we?" Ambassador Tom Rose wrote on his personal X account.
"We stand with our friends and we know how to fight and defeat our enemies!!!" he added.
Earlier Tuesday, Rose had also participated in the "March of the Living".
One million Jews and more than 100,000 non-Jews died at Auschwitz between 1940 and 1945.