The mass killing of Jews in the Holocaust was “the most heinous crime” against humanity of the modern era, Palestinian Authority President Mahmoud Abbas said Sunday, in his strongest remarks yet on the Nazi genocide.

Prime Minister Benjamin Netanyahu promptly rejected Abbas’s statements and accused him of collaborating with the Hamas organization’s efforts “to achieve another Holocaust.”

The statement comes at a sensitive time for US-led peace efforts, with Israel having suspended faltering talks last week after Abbas reached an agreement with the Islamist Hamas movement to form a unity government.

In a statement in English released just hours before Israel is to begin marking Holocaust Remembrance Day, the Palestinian leader expressed sympathy for the families of the six million Jews who were killed by the Nazi regime.

“What happened to the Jews in the Holocaust is the most heinous crime to have occurred against humanity in the modern era,” Abbas said.

He also expressed his “sympathy with the families of the victims and many other innocent people who were killed by the Nazis.”

The Palestinian leader’s remarks, made in a statement following talks with an American rabbi promoting Jewish-Muslim understanding, came as Israel and the Palestinians fought a bitter war of words over the collapse of the peace talks.

“On the incredibly sad commemoration of Holocaust Day, we call on the Israeli government to seize the current opportunity to conclude a just and comprehensive peace in the region, based on the two-states vision, Israel and Palestine living side by side in peace and security,” he said.

Netanyahu dismissed Abbas’s statement and accused him of being dishonest in his treatment of the Holocaust and contemporary threats against Israel.

He said that the Palestinian leader “last week chose to forge a pact with Hamas… a terror organization that calls for the destruction of Israel and denies the Holocaust.” Hamas, he accused, “attempts to achieve another Holocaust through the destruction of the State of Israel.”

Abbas, whose 1982 doctoral dissertation was titled “The Other Side: the Secret Relationship Between Nazism and Zionism,” has in the past been accused of denying the scope of the Holocaust. The dissertation reportedly claimed that the six million figure of Holocaust victims was hugely exaggerated and that Zionist leaders cooperated with the Nazis.

Israel will at sundown begin marking Holocaust Remembrance Day, holding memorial events and maintaining two minutes of silence to remember the victims of the Nazi genocide.