Saudi Arabia just agreed to buy Russia's S-400 missile defense system

Saudi Arabia has agreed to buy Russian S-400 air defense system, Saudi-owned al-Arabiya television reported on Thursday, on the sidelines of a visit by Saudi King Salman to Moscow.

The Dubai-based television channel also said that Saudi Arabia had signed a memorandum of understanding to help the kingdom in its efforts to develop its own military industries.

Salman arrived in Moscow on Wednesday, and it was the first time a Saudi king has ever visited Moscow.

Salman and Russian President Vladimir Putin were slated to talk about global oil market and the war in Syria, the latter of which has been a source of tension between the two nations in recent years. Moscow backs the Syrian regime, while Riyadh has supported the government's enemies.

This is also the first time in recent years, according to SIPRI, that Saudi Arabia has purchased weaponry from Moscow, as the US is Riyadh's main source of arms.

And this is the second time in the last month that Moscow has sold its S-400 missile defense system to an ally, and major purchaser of weapons, of the US. Last month, Turkey agreed to buy the S-400 defense system, which has further strained relations between Ankara and NATO.