Israeli Prime Minister Benjamin Netanyahu threatened on Monday to boycott a meeting with German Foreign Minister Sigmar Gabriel if he met with Israeli rights organizations.

Israeli officials said they would cancel the Tuesday meeting if Gabriel met with Breaking the Silence and B'Tselem as planned.

Breaking the Silence is a non-government organization that publishes testimonies of veterans from the Israeli Defense Force to shed light on the Israeli occupation of the West Bank. B'Tselem is a non-profit that documents human rights abuses in occupied territories.

"I almost can't imagine that would happen, because it would be an extraordinarily regrettable," Gabriel told German publich broadcaster ZDF on Tuesday morning, adding it would be "unthinkable" to cancel a meeting with Netanyahu in Germany if he were to meet with critics of the government.

An Israeli official said that Gabriel was welcome to meet with B'tselem, but that Netanyahu opposed a rendezvous with Breaking the Silence. Asked at a press conference on Tuesday whether he would meet with Netanyahu or Breaking the Silence activists, Gabriel said: "I hope both."

'Clear policy'

A source told local station Channel 2 news that "Israel lays down a clear policy, despite its close ties with Germany - with the aim of preventing the erosion caused by meetings between European representatives and these organizations."

"This message was clearly conveyed to the Germans," an official told "Times of Israel." The report was also confirmed by "Associated Press."

The country's Deputy Foreign Minister Tzipi Hotovely said on Twitter that she supported the ultimatum, saying it would help fight defamation of Israel.

Gabriel arrived in Israel on Monday to participate in Holocaust memorials.

Watch video 00:34 Netanyahu threatens to scrap talks

Meetings to continue

Local paper Haaretz reported that the German diplomat planned to continue with the Tuesday meetings with the two organizations. Two months ago the Belgian ambassador to Israel was summoned for an explanation following a meeting between the Belgian Prime Minister and the two organizations, the paper reported.

Gabriel said on Sunday that "unbreakable" ties between Germany and Israel formed part of Germany's national identity and pillars of its foreign policy, but said Berlin would continue to press for a two-state solution.

"With respect to the Middle East conflict, our solidarity with Israel also means working to ensure that Israel and Palestine can live side by side in dignity and peace," Gabriel said in a statement released as he departed for the region.

"Only a two-state solution will be sustainable," he said.

Strong relations with Israel have been a top priority for Germany since World War Two, in which six million Jews were systematically killed by the Nazis.

Relations have been strained following an expansion of Israeli settlements in Palestinian territories. In March German Chancellor Angela Merkel canceled a summit with Netanyahu that was due to take place in Jerusalem in May.