Tehran is currently moderately convinced that America and Israel will not dare to destroy the Iranian nuclear weapons program. This is one of the reasons for its rejectionism in Vienna. Nevertheless, on Quds Day, Hezbollah secretary-general Hassan Nasrallah threatened that Iran might attack Israel directly if Israeli sabotage operations against the Iranian nuclear weapons program continue.
Nasrallah belongs to the Arab rhetorical political tradition and therefore typically uses hyperbole, something which his comrades in arms in Tehran do not employ. Also, the Iranian regime lies only when it is religiously required (such as denying seeking nuclear weapons) while Nasrallah in contrast often lies for rhetorical and political purposes.
Why would Nasrallah warn that Iran (and of course its satellites along with it) might attack Israel in response to Israeli sabotage operations against the Iranian nuclear weapons program? The obvious reason would seem to be to deter Israel from any further such covert operations. However, if Iran planned such a surprise assault on Israel, why warn about it in advance and why have Nasrallah forward the warning?
Actually, Iran may be preparing its own preemptive Plan B. Why would they do so? The Iranians are currently moderately convinced that the Israelis and the Americans will not dare to attack the Iranian nuclear weapons program. However, if the Israelis and the Americans at some point succeed in convincing the Iranians that they are serious about terminating the Iranian nuclear weapons program, then Iran may indeed resort to their own preemptive Plan B. This does not seem very likely but the possibility cannot be entirely excluded. Twelver theology prohibits offensive warfare but according to the Islamist Weltanschauung is the presumed Jewish-American conspiracy to destroy Islam a coherent global entity and so continued Israeli sabotage operations against the Iranian nuclear weapons program may prompt Iran to lash out globally with chemical and biological weapons against nations deemed pivotal to the “octopus”. Under what circumstances could this happen? If Iran gathers intelligence proving that the destruction of the Iranian nuclear weapons program is already decided and scheduled, then Iran may decide to act preemptively and “destroy” its enemies before they can destroy the Iranian nuclear weapons program.
A surprise attack would make sense as it would catch Israel and other intended victims of Iran’s WMD apocalypse unprepared. Israel for example would likely not have the time to hand out gas masks and issue instructions for isolating windows from gas attacks. Iran and its proxies will only use chemical weapons against Israel since biological weapons would kill millions of Palestinians as well. Attacking Israel with chemical weapons without the IDF Home Front Command having made defensive preparations against chemical warfare would kill far more Israelis than would otherwise be the case and so certainly makes sense from the perspective of Tehran.
Tehran of course believes that such a cataclysmic global event would trigger the reappearance of the Hidden Imam (Mahdi) in Mecca and thus also the appearance of Jesus in Damascus and the Dajjal (Deceitful Messiah) in Jerusalem. Islam believes that the Jews will recognize the Dajjal as their Messiah and as the God of Israel and that Jesus eventually will kill the Dajjal. Khomeinist ideologues identify the followers of the Dajjal with the alleged Jewish-American global conspiracy to destroy Islam. Destroying Israel would severely weaken the forces of the Dajjal in the Middle East and would therefore be eschatologically conducive. A preemptive attack could surely be theologically justified and it would be launched specifically to deter the destruction of the Iranian nuclear weapons program and to hasten the US withdrawal from the Middle East.
It needs to be emphasized that Iran would deploy biological weapons against major US cities which likely would be delivered by submarine near the US coastline and from there handed over to agents in leisure boats who would transfer them to sleeper cells in American major cities. The United States would find it very difficult to defend itself against such attacks which would lead to potentially hundreds of thousands of dead or more. A preemptive/surprise/deterrent attack would in the peculiar Iranian view protect the nuclear weapons program and hasten a US withdrawal from the Middle East.
The governments of Israel, the United States and allied nations are so far making no efforts to alert their peoples to this danger. Perhaps they wish to avoid public hysteria and collapse of their stock markets? It is also possible that those governments are asleep at the wheel and are unaware of the danger of an Iranian preemptive wave of global WMD attacks.