German Foreign Minister Sigmar Gabriel visits Jerusalem's Hall of Remembrance on April 24. (Gali Tibbon/Agence France-Presse)

JERUSALEM — Israeli Prime Minister Benjamin Netanyahu issued an ultimatum to Germany's top diplomat, Sigmar Gabriel: Either cancel a meeting with an activist group critical of the government or meet with me. You can't do both.

Gabriel chose the activists. Natanyahu snubbed Gabriel. And an unusual diplomatic spat broke out Tuesday, with Gabriel suggesting Israel was overreacting and Netanyahu accusing Germany's foreign minister of crossing the line.

Netanyahu's office called off a meeting with Gabriel after he refused to drop his session with Breaking the Silence, a nonprofit organization that collects the testimonies of former Israeli combatants with the aim of exposing “the reality of everyday life in the occupied Palestinian territories.”

In an interview with German television network ZDF, Gabriel said it was “totally normal” to meet with groups from civil society such as Breaking the Silence. And he added that “it wouldn't be a catastrophe” if he did not meet Netanyahu, who also holds the portfolio of foreign minister. A meeting with Israeli President Reuven Rivlin went ahead on schedule.

“I think we mustn’t become part of the domestic policy game in Israel,” Gabriel told the German news agency Deutsche Presse-Agentur.

But he sprinkled in a bit of outreach in a separate statement: “What happened is not nice, Netanyahu also serves as foreign minister and foreign ministers are supposed to talk to each other in every situation. However, this will not significantly affect relations between Germany and Israel.”

Gabriel arrived in Israel on Monday, the day Israelis mark Holocaust Remembrance Day. It’s a particularly sensitive time for Jews who remember the atrocities perpetrated by the Nazi regime and the millions of Jews killed during World War II.

Gabriel took part in an official Remembrance Day ceremony, laying a wreath at Yad Vashem, the World Holocaust Remembrance Center.

Thousands of people from all over the world took part in a Holocaust memorial march on April 24, walking down a path linking the World War II Nazi death camps at Auschwitz-Birkenau in Oswiecim, Poland. (Reuters)

He had been scheduled to meet Netanyahu on Tuesday until word of his meeting with Breaking the Silence reached the Israeli prime minister.

In June, Palestinians will mark 50 years of Israel's military occupation, a situation that much of the world considers illegal.

Breaking the Silence is particularly reviled by Israel's right-wing political leaders, who say the group aims to discredit the military — sacred soldiers who give their lives for the state — and undermine the Israeli state.

[Israeli prosecutors target group that collects testimony on soldiers’ conduct]

What makes the group even more controversial for Israelis is that the identities of those who share their military experiences are largely anonymous.

In the past, the organization retold the soldiers' stories to Israeli high school students and even to active soldiers. The goal, they said, was to raise a discussion in Israeli society of the army's treatment of the Palestinian population. In recent years, however, there has been an attempt to muzzle the group.

In 2015, Israeli Education Minister Naftali Bennett, from the ultranationalist Jewish Home party, moved to ban the group from the education system. And, more recently, Israeli lawmakers have attempted to have it outlawed completely.

“Imagine if foreign diplomats visiting the United States or Britain met with organizations that call American or British soldiers war criminals. Leaders of those countries would surely not accept this,” Netanyahu wrote in a statement.

He said it was not his policy to meet foreign visitors who, on diplomatic trips to Israel, meet with groups that slander Israeli soldiers as war criminals.

“It is unacceptable, particularly during Holocaust Remembrance Day, for a visiting diplomat to meet with a group that uses anonymous testimony to discredit the Israeli army,” a senior official in Netanyahu’s bureau, speaking on the condition of anonymity because he was not authorized to speak to the media, told The Washington Post.

There had been reports that the Israeli prime minister also was opposed to Gabriel’s meeting with another left-wing, anti-occupation group, B'Tselem, but the official said that was considered less problematic.

[Israeli right goes after Israeli left in brawl over NGOs and art]

On Gabriel’s meeting with Breaking the Silence, the official said: “Israel’s prime minister would not go to Germany and meet with a group that was calling the German soldiers war criminals for their actions in Afghanistan.”