In a letter addressed to President Emmanuel Macron of France, Saudi King Salman expressed his "profound concern" with talks underway between Moscow and Doha for the sale of the advanced anti-aircraft weapon system, French daily Le Monde reported on Friday.
The Saudi monarch, who asked that France increase its pressure on Qatar, said he was worried about the consequences of Doha's acquisition of the mobile surface-to-air missile system which he said threatened Saudi security interests.
"(In such a situation), the Kingdom would be ready to take all the necessary measures to eliminate this defense system, including military action," King Salman was quoted as saying in the letter, whose content Le Monde obtained via a source close to Elysee Palace, Al Jazeera reported.
In January, Qatar's ambassador to Russia said talks for the acquisition of the air-defense system were "at an advanced stage".
This came after the signing of an agreement on military and technical cooperation between the two countries in October 2017 to further cooperation in the defense field during a visit by Russian Defence Minister Sergei Shoigu to the Persian Gulf state.
On June 5, 2017, Saudi Arabia - alongside fellow Persian Gulf Cooperation Council (PGCC) countries Bahrain and the United Arab Emirates, as well as Egypt - imposed a sea, air and land blockade on Qatar, accusing it of supporting "terrorism" and destabilizing the region, allegations Doha has consistently denied.
Among its list of demands for the resolution of the crisis, the blockading quartet asked that Al Jazeera media network and a Turkish military base be shut down.
In October, during a visit by King Salman to Moscow, the kingdom signed preliminary agreements to buy the S-400 system.
Asked whether Saudi's opposition to the deal with Qatar will affect Moscow's calculations, Pavel Felgenhauer, a Russia-based defense analyst, said this is unlikely to be the case.
"Russia has been for some years trying to build up a kind of trade relationship with Saudi Arabia but that has not really worked out at all," Felgenhauer said.
"Saudi Arabia has been clearly attaching political strings to any possible deal with buying Russians weapons ... that Russia should scale down its cooperation with Iran primarily and maybe modify its position in Syria," he added.
"Qatar is not attaching such strings (and) Russia would not militarily try to get involved in anything that's happening in the (Persian) Gulf ... in any case these anti-aircraft missiles, if they ever appear in Qatar, this won't be any time soon."