"Work will begin in the fall of this year," Kirienko said during the plenary session of the Atomexpo-2015 forum.
The new units will have two reactors of the improved water-water (VVER) design. The reactors will produce 1,000 megawatts each, tripling Iran's nuclear power production capacity.
Iran anticipates a gradual roll-back of sanctions following a final deal on its disputed nuclear program, scheduled to be signed by a group of six world powers known as P5+1 and Tehran by July 1.
Russian-built Bushehr went online in 2011 and launched at full capacity in the summer of 2014.
An agreement to expand civilian nuclear energy cooperation and construct a total of eight additional nuclear reactors at Bushehr was signed between the sides on November 11, 2014.
In September 2014, Russian nuclear experts unveiled a project for the plant's second reactor unit, Bushehr-2.