Saudi Arabia has reportedly threatened  to attack Qatar if they purchase an air defense system from Russia:
Saudi Arabia has threatened military action against Qatar if it goes ahead and acquires Russia’s top of the range S-400 air defence missile system, Le Monde daily reported.
Citing information it had obtained, Le Monde said Friday that Riyadh had written to French President Emmanuel Macron asking him to intervene to prevent the deal going ahead and to help preserve regional stability.
The Russian response has been to dismiss  the Saudi threats as irrelevant, and it appears that the sale will go ahead. The Saudi threats may be empty, but after a year of unsuccessfully bullying Qatar with their blockade they may be willing to follow through on them. The fact that the Saudis are willing to threaten another country with an illegal attack like this underscores just how reckless and destabilizing Saudi Arabia has become in the last few years. The Saudis and their allies have already devastated neighboring Yemen over the last three years, and now they threaten to use force against another neighbor without the slightest justification. U.S. indulgence has helped to encourage the Saudis to become this regional menace, so it is up to the U.S. to end its support for this reckless client .