Istanbul__ Even as Iranians on Monday demonstrated outside the old US embassy on the anniversary of the 1979 embassy seizure and hostage crisis that led to the severing of US-Iranian diplomatic ties, one former Israeli intelligence chief said he saw signs of a potential opportunity emerging from recently intensified US-Iran nuclear diplomacy.

If the US and Iran are able to reach a nuclear deal, will they move next to implement a broader rapprochement? And if so, would the prospect of a thaw in US-Iran ties lead Iran to consider reducing hostilities against Israel? Or is that a bridge too far?

"I come away from this with a sense of possibility, by no means a certainty, that there might be an opening, in which one can turn around the thorniest problem of all: the deep-seated rejection of Israel by the current regime in Iran," Efraim Halevy, former head of the Israeli intelligence service the Mossad, told Al-Monitor in interviews on the sidelines of a conference on Middle East security issues in Istanbul this week convened by the Pugwash Conference on Science and World Affairs. "This will not be obtained overnight."

"If the Iranians think straight, ..they must realize it is inconceivable that they [would be] able to change the basics of the relationship between Iran and the US whilst maintaining the level of denial and enmity they now have to Israel," said Halevy, who conducted secret negotiations with Jordan's King Hussein that led to the historic 1994 peace treaty between the two countries.