"All our military cooperation with Iran is totally within the international law, including the UN Security Council armaments resolutions and Russian legislation. We are acting very responsibly when it comes to Iran," Russia Today quoted Sergey Ryabkov as saying.
However, Iran's Defense Minister Mostafa Mohammad Najjar said Wednesday that Tehran would elaborate on the potential Russian sale of advanced surface-to-air missiles "when the occasion presents itself", press tv reported.
He added that Iran would never hesitate in purchasing any cutting-edge equipment that it deems necessary for its defense, while noting that any new developments in this field would be made public when the time is right.
His remarks came a day after Washington pressed Russia to end the confusion surrounding the delivery of the strategic S-300 system to Iran.
There were also reports a week ago that Russia had already started to supply S-300 systems to Iran, raising concerns in the US and Israel.
Russia's state-run arms exporter Rosoboronexport confirmed on Monday that it is supplying Iran with a number of defensive systems.
Although Rosoboronexport did not elaborate on whether the defensive apparatus include the sophisticated long-range S-300 missiles, it asserted that any Russian sale to Iran would be "solely of a defensive nature".
"Russia is developing military-technical cooperation with Iran in strict compliance with its international commitments stemming from nonproliferation agreements. This cooperation cannot be a source of concern for third countries," said the Monday statement.
However, Israel and the US oppose any such deal. Tel Aviv has taken measures to dissuade Russia from providing Iran with the S-300 system which, according to Israeli and American intelligence sources, would make Iran's nuclear infrastructure inviolable in the face of an Israeli attack.
Pentagon consultant Dan Goure says the delivery of the system "scares every Western air force." According to Goure, the report of any S-300 delivery could prompt a premature Israeli air attack.
Israel has threatened to strike Iran's nuclear facilities, claiming Iran is developing a military nuclear program. Tehran insists its program is directed at the civilian applications of the technology.
The S-300, capable of destroying ballistic missiles, is considered one of the most advanced anti-aerial weapons in the world. It is a Russian-made long-range surface-to-air missile system. It was developed to defend against aircraft, cruise and ballistic missiles.
Its radar has the ability to simultaneously track up to 100 targets while engaging up to 12. S-300 deployment time is five minutes. The S-300 missiles are sealed rounds and require no maintenance over their lifetime.
The UN nuclear watchdog has certified "the non-diversion of declared nuclear material in Iran". It, however, continues to urges Tehran to increase nuclear cooperation and disclosure.