As the Obama administration prepares to engage Iran diplomatically, a number of questions dominate the debate on how to deal with Tehran's revolutionary regime.

Should the Western democracies accept Iran's President Mahmoud Ahmadinejad, the man who denies the Holocaust happened and calls for Israel to be "wiped off the map", as a legitimate negotiating partner?

Is Ahmadinejad the real decision-maker in Tehran? Is the Islamic Republic truly determined to develop nuclear weapons? What motivates the Khomeinist leaders and militants? Is there any way in which the outside world could avoid confrontation with Iran?

These and many other questions are raised in two new books on Iran as it marks the 30th anniversary of the Khomeini revolution.

Con Coughlin's new book, Khomeini's Ghost: The Iranian Revolution and the Rise of Militant Islam (Macmillan), proposes to answer the crucial question of who has the final word in Tehran. He identifies the Supreme Guide, Ayatollah Ali Khameini - rather than the President as the final decision - maker in the Islamic Republic and thus the ideal negotiating partner for Obama.

"The powers entrusted to the Supreme Guide...compare favourably with those claimed by Europe's fascist dictators...with the added benefit of claiming divine inspiration." After the Supreme Guide, Coughlin suggests the Islamic Revolutionary Guard (IRG), the parallel army created by the mullahs to protect the regime, as key in shaping Iran's domestic and foreign policies.