It is hard to see how Saudi Arabia’s New Year execution spree will send the signal it presumably intended: that of an absolute monarchy on which the sun will never set, laying down the law on its own terms with a sanguinary warning to would-be predators at home and abroad. It looks, instead, like a defensive message that injects yet more sectarian venom into the cauldron of the Middle East. That poison is not something the House of Saud or the Wahhabi clerical establishment that legitimises it can control, as the Sunni-Shia conflict they help incite keeps ripping the region apart.

Ever since last year’s nuclear deal between international powers led by the US and Iran, the kingdom’s arch-rival, started to look unstoppable, Saudi leaders appear to have reached three conclusions. Yes, they have been outplayed diplomatically and feel let down by their long-term American ally and patron. To their north — and in good part because of what they see as US bungling and lack of backbone, first in Iraq and then Syria — Tehran has cut a Shia arc through Arab lands from Baghdad to Beirut. They have repeatedly told Washington they regard what they see as Iran’s spearheading of a Shia jihad in the region as a greater threat than the Sunni jihadi menace of Isis.

Thus Riyadh seems determined to ensure any Iran-backed incursion into the Gulf is off limits. The message is that the Arabian peninsula is terra sancta for (Sunni) Islam, which the House of Saud presumes to lead worldwide. There will be no Persian encroachment, and no quarter for local Shia — always abominated as idolaters by Wahhabi bigots but long seen by the Saudi government as fifth columnists for an Iran radicalised by its 1979 Islamic Revolution. The already dim prospect of a negotiated transition out of Syria’s civil war fades in the burning light of rekindled Saudi-Iranian enmity.