The demonstrations, which began Dec. 28 over the country's struggling economy, have been the largest in Iran since the disputed 2009 presidential election. At least 21 people have been killed and hundreds arrested.
Montazeri said the CIA official sought help from exiled Iranian groups and prepared for various scenarios that included protesting the high cost of living and financial demands on the elderly. Some received intelligence support from Israel and financing from Saudi Arabia -- Iran's two biggest regional adversaries.
The plot focused on fomenting dissent from the countryside to shake Tehran, Montazeri said.
Iranian suspicion of the CIA stretches back to 1953, when the CIA and the British executed the coup that overthrew its elected prime minister and cemented the rule of the American-backed shah.
A top Russian diplomat warned the U.S. not to meddle in Iran's affairs and suggested that Washington wants to use the unrest to undermine the Iran nuclear agreement.