The Prime Minister exclaims "Benny Gantz, you should be ashamed", and added "you are attacking me, an officer and combat soldier in the Sayeret Matkal command unit, in which I risked my life several times for the state, participated in different operations and was wounded in the 1972 operation to rescue the hostages from the Sabena plane hijacking".
Meanwhile, an Israeli government official confirmed that a planned meeting in Moscow between Netanyahu and Russian President Vladimir Putin has been postponed.
Retired military chief Benny Gantz of the Resilience party and ex-finance minister Yair Lapid, head of the Yesh Atid party, said they would present a joint list for the upcoming Israeli elections that "will constitute the new Israeli ruling party".
Ben Gvir, a member of Jewish Power, said his faction "put personal honour aside" to prevent Netanyahu's main election rival from forming a government.
Signaling his concern over this new development, Netanyahu's Likud immediately issued a statement claiming that a government led by Gantz and Lapid would quickly reveal itself to be left-wing in policy and push an Arab-driven agenda.
"In light of the union in the left, I urge Prime Minister Netanyahu to make an act of leadership and call on Moshe Feiglin's Zehut, Moshe Kahlon's Kulanu and Avigdor Liberman's Yisrael Beytenu-three parties that now fail to pass the electoral threshold-to merge into one bloc, ensuring not a single Knesset seat goes to waste", Bennett said.
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In addition to voting to merge with Otzma Yehudit, the Jewish Home central committee also approved ongoing negotiations with Yachad chairman Eli Yishai, Times of Israel reported.
The prime minister is also under pressure ahead of an announcement by Israel's attorney general on whether to indict Netanyahu after police recommended charging him in connection with three corruption cases.
Following them in the joint list would be a pair of other former military chiefs, Gabi Ashkenazi and Moshe Yaalon. For the first two thirds of the term Lapid would be foreign minister with defense minister reserved for Moshe Yaalon.
On Wednesday, Netanyahu helped negotiate the merger of two far-right parties, the pro-settler Jewish Home and the racist Jewish Power, that could give followers of the late anti-Arab rabbi, Meir Kahane, a stronger voice in politics.
"The new ruling party will bring forth a cadre of security and social leaders to ensure Israel's security and to reconnect its people and heal the divide within Israeli society", the party said in a statement.
Netanyahu's Twitter account reacted to the merger with multiple posts indicating the choice was clear for Israeli voters between "a weak left government" and a country that was "flourishing" under his leadership.
Even if the joint list surpasses Likud at the ballot box, it is not guaranteed to form the next government unless it can garner a parliamentary majority with other parties.