Jan 30 (Reuters) - The United States is considering new military strikes against the Islamic Republic of Iran over its deadly suppression of protests this month.

The complexities of Iran's ruling system, the ideological nature of its support base, and the power of its Revolutionary Guards make it hard to predict its resilience or vulnerability in the face of external attack, or what might come next.

The following explains how the system operates and who the main figures are in today's Iran:

WHY DOES IRAN HAVE A 'SUPREME LEADER'?

Iran's political system is based on the theory of vilayat-e faqih ("rule of the jurist"), which holds that until the return of the Shi'ite Muslim 12th Imam, who disappeared in the ninth century, power on earth should be wielded by a supreme cleric.

The first Supreme Leader, Ayatollah Ruhollah Khomeini, was the charismatic father figure of the 1979 Islamic Revolution who developed the model of a cleric standing above an elected government.

His successor, Ayatollah Ali Khamenei, has cemented that role since becoming leader in 1989. This has ensured he retains the ultimate say on all major policy decisions and has built a parallel system of rule, alongside that of the elected government, staffed with loyalists.

Khamenei's sway has often been wielded through the National Security Council headed by longtime adviser Ali Larijani. Other advisers to Khamenei, including former defence minister Ali Shamkhani and former foreign minister........

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