An estimated 16-20 million Iranians would die in a nuclear war with Israel, according to a report issued by a respected Washington think tank.
The Center for Strategic and International Studies (CSIS) also estimates that between 200,000 and 800,000 Israelis would be killed, the Jerusalem Post reported.
The report, which is theoretical and based on limited verified knowledge of Israel's and Iran's nuclear capability, paints a bleak picture for both nations.
It estimates that a nuclear war would last approximately three weeks and ultimately end with the annihilation of Iran, based on Israel's alleged possession of sophisticated and powerful nuclear weapons.
The report does not predict the number of deaths due to nuclear fallout.
It lists possible targets for an Iranian strike as Tel Aviv and Haifa, while the list of probable targets in Iran includes Tehran and Tabriz.
The report also points to Israel's Arrow missile defense system as an obstacle facing any Iranian strike.
Another scenario includes Syria coming to Iran's defense with chemical and biological warheads launched at Israeli targets. Up to 800,000 Israelis would be killed if that were to happen, according to the report. Syria, however, would be forced to grapple with the deaths of approximately 18 million of its citizens if Israel responded with its nuclear arsenal, the Post reported.