If anyone had doubts that Syria's gruesome civil war is already spinning into a wider Middle East conflict, the events of the past few days should have laid them to rest. Most ominous was Israel's string of aerial attacks on Syrian military installations near Damascus, reportedly killing more than 100.

The bombing raids, unprovoked and illegal, were of course immediately supported by the US and British governments. Since Israel has illegally occupied Syria's Golan Heights for 46 years, perhaps the legitimacy of a few more air raids hardly merited serious consideration.

But it's only necessary to consider what the western reaction would have been if Syria, let alone Iran, had launched such an attack on Israel – or one of the Arab regimes currently arming the Syrian rebels – to realise how little these positions have to do with international legality, equity or rights of self-defence.

Israeli officials have let it be known that the attacks, launched from Lebanese airspace, were aimed at stockpiles of Iranian missiles bound for Hezbollah, the Lebanese Shia resistance movement and governing party. They were not, it was said, intended as an intervention in Syria's civil war – but as a warning to Iran and protection against Hezbollah attacks in a future conflict.

That's not how it seemed to the Syrian rebel fighters on the ground, filmed greeting the attacks with cries of "Allahu akbar", unaware of who had actually carried them out. By bombing the Syrian army, which has recently made advances in some rebel-held areas, Israel is clearly intervening in the war.

The raids follow the public declaration by Hezbollah's Hassan Nasrallah last week that his fighters are supporting government forces inside Syria – which are also backed by Iran, Russia and China. It is Syria's role as the pivot of Iranian influence across the Middle East that has turned the Syrian war into a potential regional conflagration.

Having hedged its bets, Israel has now started to make clear it regards the prospect of Islamist and jihadist groups taking over from the Assad regime as less threatening than the existing "Syria-Iran-Hezbollah axis", as the Israeli defence ministry official Amos Gilad put it recently.

That has coincided with talk of creating an Israeli buffer zone inside Syria, while Israeli officials have been pushing claims that the Syrian regime has used chemical weapons. Since Obama declared that the use of chemical weapons would cross a "red line", allegations of their use have become a crucial weapon for those demanding increased western intervention, in a bizarre echo of the discredited orchestration of the invasion of Iraq a decade ago.

That effort came unstuck this week when the UN investigator Carla Del Ponte reported that there were "strong concrete suspicions" that Syrian rebels had themselves used the nerve gas sarin. The claim was hurriedly downplayed by the US, though the rebel camp clearly has an interest in drawing in greater western intervention, in a way the regime does not.

The fact is intervention has long been a central dimension of the war. The regime forces are backed by Syria's old allies in Russia and Iran. Funding and military support for the rebels come from the US, Britain, France and their regional allies: Turkey, Saudi Arabia, the UAE, Qatar and Jordan.

Airlifts of arms to the Syrian rebels, co-ordinated by the CIA, have increased sharply in recent months to become what one former US official calls a "cataract of weaponry". British and American forces are training rebel fighters in Jordan. The worth of US aid to the Syrian opposition has doubled to $250m, while the EU has now lifted its oil embargo to allow exports from rebel-held areas.

The result of foreign intervention has of course been to escalate the conflict. Now pressure is building on the Obama administration to go further and supply weapons directly. Among those pushing for more intervention is David Cameron – anxious to ingratiate himself with the Gulf dictators – who has been pressing for the EU arms embargo to be lifted.

The intention is to build up the west's favoured groups and weaken the role of jihadists who have taken centre stage as the war has gone on. They include Jabhat al-Nusra, which now controls swaths of rebel-held territory and has declared allegiance to al-Qaida.

The irony of the US and other western governments – let alone Israel – once again making common cause with al-Qaida, after a decade of a "war on terror" aimed at destroying it, is one factor holding Obama back. So is the risk of being drawn into all-out war (publicly raised by Britain's chief of the defence staff); the hostility of American public opinion (mirrored in Britain and the Arab world); and the aftermath of intervention in Libya, where militias have been besieging government offices demanding the ousting of western-backed Gaddafi-era leaders.

The reality is that what began in Syria more than two years ago as a brutally repressed popular uprising has long since morphed into a vicious sectarian war, manipulated by outside forces to change the regional balance of power and already dangerously spilling over into neighbouring Lebanon and Iraq.

The consequences for Syria have been multiple massacres, ethnic cleansing, torture, a humanitarian crisis and the risk of the country's breakup. The longer the war, the greater the danger of a Yugoslavian-style fragmentation into sectarian and ethnic enclaves.

The Assad regime bears responsibility for that, of course. But so do those who have funded and fuelled the war, bleeding Syria and weakening the Arab world in the process. The demand by Cameron and other western politicians to increase the flow of arms is reckless and cynical.

The result will certainly be to ratchet up the death toll and spread the war. If they were genuinely interested in saving lives – instead of neutralising Syria to undermine Iran – western leaders would be using their leverage with the rebels' regional sponsors to negotiate a political settlement that would allow Syrians to determine their own future.

That would be difficult enough to achieve and enforce on the ground. But an internationally and regionally backed deal now looks the only way to bring the war to an end. In which case, increased intervention is really about improving the west's bargaining hand, at a cost of yet more Syrian suffering – and yet another backlash to come

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