US Vice President Joe Biden and Secretary of State John Kerry both met informally with Zionist Camp co-leader Isaac Herzog — head of the Labor Party and Prime Minister Benjamin Netanyahu’s chief rival in the Israeli elections — on the sidelines of a security conference in Munich, Germany on Saturday.

Their discussions reportedly revolved around security matters and the Zionist Camp’s defense strategy.

The meetings were not formally scheduled, and no photographs were immediately issued.

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Herzog also met with the EU’s Foreign Affairs Chief Federica Mogherini and German FM Frank-Walter Steinmeier on the sidelines of the conference.

The Biden-Kerry meetings with Herzog came a day after Biden’s office said the vice president would be abroad and would not attend a contentious speech on Iran Netanyahu is set to deliver to Congress on March 3. Netanyahu’s planned address has infuriated the Obama administration, which accused the Israeli leader of breaching protocol as the visit was not coordinated with the White House. Both Kerry and President Barack Obama said last month that they would not meet with Netanyahu during the visit, citing its proximity to the March 17 elections.

Speaking to Israel’s Channel 10 after his Munich talks, Herzog underlined the scope of the crisis in ties between Netanyahu and the Obama Administration. Netanyahu “won’t get to meet with a single American official on this visit — not from the National Security Agency, not from the White House, not from the State Department,” Herzog said. “It’s a complete boycott [of Netanyahu by the Obama administration]. Even if that’s not stated, that’s the story.”

As president of the Senate, Biden would typically attend the joint meeting, putting the White House in a bind because of its irritation with Netanyahu. Biden’s overseas trip allows the White House to avoid the awkwardness of having the vice president sit behind Netanyahu during the address. It’s unclear where the vice president plans to travel, though his office said the unspecified trip was in the works before the prime minister’s trip was announced.

Netanyahu has been under increased pressure to cancel the speech, in Israel and in the United States.

Herzog said earlier Saturday that the premier must cancel his trip to the US due to the antagonism his address — which was coordinated with House Majority Leader John Boehner — has caused in Washington.

“The time has come when Bibi (Netanyahu) must announce the cancellation of his visit to Congress,” Herzog said in a speech at the conference in Munich. “In conversations I’ve held with many European and US leaders, it is clear there is great anger over Netanyahu diverting the discussion on Iran’s nuclear program for political gain, and turning it into a confrontation with the president of the United States.”

“This speech that was born in sin, as an electioneering ‘production,’ endangers the security of Israel’s citizens and the special relationship between Israel and the US,” Herzog charged.

Many Democrats also object to Netanyahu’s speech, for three reasons: The invitation is an implied rebuke for Obama; the speech, scheduled two weeks before Israel’s elections, might be designed to boost Netanyahu’s re-election hopes; and Netanyahu backs new sanctions on Iran that the administration and Western powers argue could scuttle sensitive negotiations over Iran’s nuclear program.

Rep. G.K. Butterfield of North Carolina called Boehner’s actions unprecedented, and said Netanyahu has “politicized” his US visit.

On Friday, an Israel Channel 10 TV report said that some 40 Democratic legislators were expected to stay away from the address, and that Netanyahu was anxious to avoid that spreading to a wider “second wave” of legislators. By Saturday, it said 60 legislators might stay away.

The Friday report also said that Netanyahu has conveyed messages to the Americans to the effect that “he didn’t know” the invitation extended to him to speak before the US Congress was anything but genuinely bi-partisan.

Netanyahu remains determined to go ahead with the address, to highlight the dangers of a deal that would leave Iran as a nuclear threshold state, but is making an effort “to soften” the Obama administration’s anger, and that of many Democrats, over the March 3 speech, the TV report said.