Iran has yet to complete construction of its first nuclear power plant and has previously sent conflicting signals about the state of work on a planned second plant. An Iranian official said this year construction work had already begun.
The Islamic Republic is embroiled in a dispute over its nuclear plans, which the West says are to build atomic warheads but Tehran insists are aimed at generating electricity.
"We are involved in the design phase of this power station," the deputy head of Iran's Atomic Energy Organisation, Mohammad Saeedi, said, referring to plans for a second plant to be built in the area of Darkhovin in southwest Iran.
"Gradually the complementary design phase and its building will begin," Saeedi said of the 360 megawatt plant, in comments carried by the official IRNA news agency.
"The site has been chosen and the preparation process is under way," he added.
The country's first nuclear power plant, with 1,000 megawatt capacity, is being built by Russia in the port city of Bushehr. Iran has said it wants to build nuclear power plants with a total capacity of 20,000 megawatt by 2020.
Iranian officials say Iran, which sits on the world's second biggest reserves of gas and oil respectively, wants nuclear energy so it can export more of its hydrocarbons.
The International Atomic Energy Agency (IAEA), which carries out routine inspections of Iran's nuclear facilities, has mentioned the Darkhovin project in previous reports on Iran.
Bushehr power plant has been hit by years of delays. Russia delivered fuel for the plant this year. The head of Russia's nuclear energy agency, Sergei Kiriyenko, is expected to visit Iran in September to discuss a start up date, IRNA reported.
Asked about Kiriyenko's visit, Saeedi said: "We are negotiating in order to determine the time of his trip to Iran."
Iran has been holding several rounds of talks with senior IAEA officials for clarification about intelligence reports that suggested Iran illicitly tried to design atomic bombs. Iran has said it is not the IAEA's job to delve into such allegations.
Asked about the talks, Saeedi said: "Iran will try to answer the agency's questions within the framework of its commitments. Our ties with the International Atomic Energy Agency are continuing and are on the basis of our legal commitments."