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 S-400 is Russia's most advanced long-range anti-aircraft missile system and can carry three types of missiles capable of destroying targets, including ballistic and cruise missiles.
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The organization was established after the 50-day Gaza war of 2014 when more than 2,100 Palestinians, mostly civilians, were killed.
The Kremlin said on Monday that talks with Saudi Arabia over Moscow supplying Riyadh with advanced S-400 air defence missile systems had gone well so far despite talk of a possible U.S. -Saudi arms deal.
Saudi Arabia is a semi-continent that needs to protect is land, air and marine borders through possessing air defense capabilities and other weapons that will enable it to lead tactical military work, he explained.
He said that Saudi Arabia will cooperate with Moscow in the fight against terrorism.
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But they were continuing to investigate "whether anybody else may have known about this incident before he carried it out". The Australian citizen of Filipino heritage is cooperating fully with authorities, her lawyer said.
The U.S. State Department approved a $15 billion U.S. sale for the Terminal High Altitude Area Defense (THAAD) system to Saudi Arabia.
"Our relations with the United States are strategic, but we also want to improve our relations with Russia, because good relations with the United States, Russia and China are in the interest of our country and for the Middle East and the whole world".
"This sale furthers United States national security and foreign policy interests, and supports the long-term security of Saudi Arabia and the Gulf region in the face of Iranian and other regional threats", the agency said.
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The Oscar-nominated Woods (for Ghosts of MS and Salvador ) is selling one of his four homes in Rhode Island. The actress tweeted "the dethroning continues" upon news of his retirement.
Earlier, Saudi Arabia concluded a deal worth billions of dollars with the USA.