Lebanon, “the house of many mansions”, has endured an apparently endless series of wars and crises. Now its foundations are shaking once again. The tectonic plates have shifted anew with Iran’s rise, and now this tiny, fragile state is at the heart of the struggle between the two great regional powers and other major players.

On Thursday, Saudi Arabia urged its citizens to leave Lebanon immediately after days of tensions that broke through the surface last weekend with the shock resignation of the prime minister, Saad Hariri, who blamed Iranian influence and said he feared assassination. That he made his uncomfortable statement from Riyadh – and remains there – reinforced the assumption that he had been strong-armed into doing so. On the same night came the announcement that a missile had been shot down close to Riyadh. Yemen’s Houthi rebels claimed responsibility, but Saudi officials quickly drew the line to Hezbollah and its patron Iran for this “act of war”. There are fears the standoff could escalate into an outright military clash.

Underlying all this is Riyadh’s concern that Iran, its ambitions sped by its intervention to support Bashar al-Assad and the fight against Islamic State, is only months away from completing its establishment of a “Shia crescent” across the region. That fear, which stirs ancestral anxieties in the Middle East, is shared by a US administration that has abandoned Barack Obama’s turn towards Tehran – if not yet the accompanying nuclear deal – and by Israel, which has a still more immediate concern. If it hoped the war in Syria would weaken Hezbollah, it has been disappointed: the opposite has happened. Israel looks across its borders at a confident, well-armed and very close foe. For months there have been growing warnings of another war like 2006’s devastating conflict.

These converging interests, and Iran’s closeness to achieving unprecedented influence, all point in an alarming direction. The personality of the players, notably Saudi Arabia’s extraordinarily confident new crown prince, Mohammed bin Salman, and his eager backer Donald Trump, adds an extra dimension of risk. He has given a blank cheque to the Saudi crown prince, even if some in the administration are still trying to use US influence to rein in Riyadh.

The crown prince has already led the charge into a disastrous war in Yemen which is draining Saudi coffers by billions each month, apparently at little cost to Iran, whose support for the rebels has been much exaggerated. His attempts to coerce Qatar into line have failed. If he has a game plan in Lebanon it is not clear: Mr Hariri’s resignation highlights Hezbollah’s power, but who will replace him? That is one reason some fear a physical intervention. The French president’s trip to the Saudi capital suggests that at least some are trying to calm the waters, but how much influence Europe can exert remains to be seen. Russia’s plans and interests in the region are another critical, and opaque, issue.

But if Israel and Saudi Arabia are coordinating, my enemy’s enemy is not always much of a friend. For a pillar of the Islamic world to engage in an overt alliance with Israel would be extraordinarily risky. Each side would like the other to do the hard work – and neither is keen to oblige, fully aware of the potential costs. Riyadh’s very public interference in Lebanon has if anything made it harder for Israel to act. Meanwhile, the Iranians have no desire to sabotage themselves by getting dragged into open conflict when they are so close to their goal. All know that a war could prove not just very bloody but unpredictable and uncontrollable.

All that offers reassurance of a sort: a very poor sort. In such tense situations there is always the danger that misjudgments, misinterpretations and plain old mistakes will spark a conflagration. But even if that is avoided, tensions have been ratcheted to their highest level since 2006. De-escalation is not in sight. Dodging a war is not a solution; only a deferral.