Iran builds three Ghadir-class submarines, which can fire missiles and torpedoes and operate in the Persian Gulf's shallow waters.
Iranian state TV said the country has added three more domestically-built submarines to its naval fleet.The report on Sunday said the vessels were delivered to the Iranian navy in southern port of Bandar Abbas.
It said the submarines were from the Ghadir class, of which Iran already has four.
This class of submarine can fire missiles and torpedoes and operate in the Gulf's shallow waters.
The move is seen as part of Iran's effort to upgrade its defense capabilities amid escalating tension over its nuclear program.
The West suspects Iran is aiming at developing nuclear weapons, a charge Iran denies.