He went on to advise the Shah from 1965 to 1968, he was secretary general of the Regional Cooperation for Development organization, which worked to foster economic integration among Iran, Pakistan and Turkey.

When OPEC set up its office in Geneva in 1961 before moving to Vienna Rouhani was elected the organization's first secretary general, an administrative post that also involved mediating between conflicting factions.

OPEC's success has long been a matter of debate, with many analysts saying that the marketplace and the willingness of one country, Saudi Arabia, to limit output have been the deciding factors in determining oil prices.

In 1964 Rouhani was succeeded by an Iraqi, Abd ar-Rahman al-Bazzaz, who encouraged talk of both radical politics and Islamic religion.

Rouhani played the tar, a traditional Persian musical instrument, and was an accomplished pianist and co-founder of the Philharmonic Society of Tehran.