BBC Tehran correspondent Jon Leyne says Sunday's announcement is a massive act of defiance likely to bring forward direct confrontation over Iran's nuclear programme.This isn't merely to produce sufficient enriched uranium for civilian purposes, but one that would produce enough enriched uranium for nuclear weapons.
Iran says the new plants would be of a similar size to its main existing one at Natanz.
President Mahmoud Ahmadinejad told his cabinet that parliament had ordered that Iran should produce 20,000 megawatts of nuclear energy by 2020.
It therefore needed to make 250-300 tonnes of nuclear fuel a year, he said, which would require 500,000 centrifuges for enriching uranium.
Natanz has nearly 5,000 working centrifuges, with plans to build 54,000 in all.
Under the plan Mr Ahmadinejad presented to the cabinet, the level of enrichment would also be increased.
Such a move would be in direct contravention of UN Security Council resolutions, our correspondent says, though Iran counters that it is simply doing what is allowed under the nuclear non-proliferation treaty.
And there's a complete lack of will to contain Iran's nuclear ambitions.