Russia is modernising its S-300 anti-aircraft missile system to supply to Iran, a Russian presidential adviser told RIA news agency.
"It has partially been updated, separate elements are still being updated," said Vladimir Kozhin, presidential military adviser.
"It will be that very S-300 complex that Iran wanted to receive," reports Reuters.
Kozhin did not specify a date on which the missiles will be sold to Iran.
Russia cancelled a delivery of the missiles to Iran in 2010, amid sanctions imposed on Iran by six world powers in response to its alleged attempts to develop nuclear weapons.
After an interim deal was reached between Iran and the US-led bloc, Russian president Vladimir Putin announced in April that a self-imposed ban on supplying Iran with the missiles would be lifted.
In the wake of the announcement, Israeli prime minister Benjamin Netanyahu expressed dismay that Russia had reached the missile deal with Tehran.
Israel, which opposes the nuclear deal, has previously threatened to launch air strikes on Iranian nuclear facilities, and it is feared the missile system could be used to block air strikes.
An Iranian source told Russian news agency Sputnik that "if Iran gets the S-300 system or other modern system, it will be possible to say that the sky over Iran is protected against any airstrike".