The approval opens the way for Saudi Arabia to purchase 44 Terminal High Altitude Area Defence (THAAD) launchers and 360 missiles, as well as fire control stations and radars.
Russia's Federal Service for Military and Technical Cooperation has officially confirmed the conclusion of the deal with Saudi Arabia on the supply of S-400 surface-to-air missile systems and other weapons.
"We can speak only for ourselves", said Peskov.
This sale is likely to further U.S. national security and foreign policy interests and support the long-term security of Saudi Arabia and the Gulf region.
The THAAD - Terminal High Altitude Area Defence - missile system is used to defend against incoming missile attacks and "is one of the most capable defensive missile batteries in the United States arsenal and comes equipped with an advanced radar system", according to AFP.
Iran, whose hostile behaviour has got the U.S. and Saudi Arabia concerned recently, also happens to have one of the biggest ballistic missile programs in the Middle East.
"The proposed sale of this equipment and support will not alter the basic military balance in the region", it said.
"THAAD's exo-atmospheric, hit-to-kill capability will add an upper-tier to Saudi Arabia's layered missile defense architecture".
Last week, Australia said it will outfit its new naval warships with Lockheed's Aegis air-defense system, which is also used by the US and Japan and would help the three navies coordinate on missile-defense missions.
During the first visit by a Saudi king to Russia, King Salman bin Abdul Aziz and Russian President, Vladimir Putin, underlined the rapprochement between the two countries by signing important agreements in the military and energy fields.