A Saudi official has commented on Moscow's role in the Middle East following the "landmark" visit of the Saudi King to Russian Federation last week.
The approval opens the way for Saudi Arabia to purchase 44 Terminal High Altitude Area Defense (THAAD) launchers and 360 missiles, as well as fire control stations and radars.
U.S. military sales to Saudi Arabia has come under increased scrutiny as a Saudi-led coalition is involved in military intervention in Yemen.
The deal includes contracts to purchase Russian advanced S-400 air defence systems, the Kornet Anti-Tank Missile systems, TOS-1 A rocket launchers, IGS-30 grenade launchers and AK- 103 Kalashnikov machine guns, Saudi Press Agency, SPA reported.
The department said the sale of the equipment to the Saudi people would help provide a balance to a relatively unstable environment in the Gulf and to help the USA forces enlarge its allied grip on the region.
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U.S. THAAD system equipment in Seongju, South Korea, last month.
"THAAD's exo-atmospheric, hit-to-kill capability will add an upper-tier to Saudi Arabia's layered missile defense architecture".
Despite increasing coverage over Saudi Arabia's involvement in the September 11, 2001 attacks, the two countries share an interest over Iran's ballistic missile program in the Middle East.
Both Washington and Saudi Arabia accuse Tehran of aggressive and disruptive behavior in the region.
Officials told AFP that the sale, which can go ahead if the US Congress does not object within 30 days, should be seen as part of an overall $110 billion arms package that President Donald Trump promised the Saudi kingdom during a visit in May.