Saudi Arabia, one of the countries blockading Qatar, has threatened military action against its Gulf neighbour if it acquires the Russian-made S-400 air defence system, French daily Le Monde reported on Friday.

In a letter addressed to President Emmanuel Macron of France, Saudi King Salman expressed his “profound concern” with talks under way between Moscow and Doha for the sale of the advanced anti-aircraft weapon system.

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 defence 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.

Year-long blockade

In January, Qatar’s ambassador to Russia said talks for the acquisition of the air-defence 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 defence field during a visit by Russian Defence Minister Sergei Shoigu to the Gulf state.

On June 5, 2017, Saudi Arabia – alongside fellow Gulf Cooperation Council (GCC) 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 destabilising 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 defence analyst, told Al Jazeera that 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 Gulf … in any case these anti-aircraft missiles, if they ever appear in Qatar, this won’t be any time soon.”