In mid-2013, Prime Minister Benjamin Netanyahu rejected a proposal from the Sultanate of Oman to mediate a back channel between Israel and Iran, believing it would legitimize the secret U.S.-Iran talks that ultimately led to the 2015 nuclear deal, according to four former Israeli officials involved in the negotiations.

Why it matters: Knowledge of the dramatic Omani initiative had until now been restricted to a small group of Israeli officials. When he came into office in 2009, Netanyahu banned the Israeli Mossad from engaging in any direct or indirect talks with the Iranians without his clear approval, Israeli officials told me. Such an order doesn’t exist for any other country in the world.

The backdrop: In early 2013, Israel discovered that the U.S. and Iran were holding secret talks behind its back in Muscat, Oman.

Yaakov Amidror, who was then Netanyahu’s national security adviser, told me he protested to his American counterpart Susan Rice at the time, telling her it was insulting that the U.S. thought Israel wouldn't find out about the secret U.S.-Iran back channel in Oman.

"I was disappointed that the Americans more or less cheated us and I told them that," Amidror said.

In May 2013, after Hassan Rouhani — who is perceived by many as a moderate — won the presidential elections in Iran, the Sultan of Oman Qaboos bin Said sought to move forward into the second part of his initiative and promote Iranian-Israeli talks under his auspices, former Israeli officials told me.

Several weeks after Rouhani’s victory, the then-director of Mossad Tamir Pardo arrived at his weekly meeting with Netanyahu and presented him with sensitive information from the Sultanate of Oman, according to the former officials.

Israel and Oman had a secret relationship that started five decades ago, and the Omanis had a very good reputation for being discreet and effective mediators.

Behind the scenes: According to the former Israeli officials, the director of Mossad told Netanyahu the Sultan of Oman proposed establishing a secret back channel between Israel and Iran that would enable the parties to talk to each other and de-escalate tensions.

The officials said the Omanis thought Rouhani’s victory opened a window of opportunity and that U.S.-Iran talks could yield better results if Israeli-Iranian negotiations were taking place at the same time.

The message from Oman to Israel at the time was, “Even if you don’t agree on anything, engagement leads to de-escalation and non-engagement could lead to war,” according to the former Israeli officials.

Netanyahu heard what Pardo had to say and got national security adviser Amidror into the picture. Amidror told me the Omani interest was to be involved in everything and show that they could be effective mediators, but Israel had to consider whether the proposal served its interests.

Pardo and a group of senior Mossad officials thought the Omani initiative was serious and that Israel should at least explore the possibility of talks with Iran.

Amidror was vehemently against the idea, and told me: "The whole purpose of the Omani initiative was to give cover to the Iranians and the Americans who cheated us."

Netanyahu had more meetings with Pardo and with Amidror and eventually decided to reject the Omani initiative. Amidror still believes that the Mossad position was wrong and that Netanyahu was right to say no to the proposal.

“The Israeli response to the Omanis was warranted — as long as the Iranian leadership seeks to destroy us, we have got nothing to talk about with them," Amidror told me.

The other side: Other former Israeli officials who were deeply involved in the affair still believe today that the Omani proposal was genuine, that the Iranians would have played ball and that it was a missed opportunity for de-escalation.

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