Carnage in Jisr al-Shughour has taken the Syrian crisis to a new level, even as Bashar al-Assad's regime descends to new depths. Three risks now stand out. The first and most obvious is vicious regime retaliation against residents of the north-western town where 120 army and security personnel are said to have been killed. The second is the very real spectre of civil war raised by this escalation. Third, and most dangerous for Israel and the west, are growing, linked attempts by the regime and its ally Iran to externalise the conflict.

Syrian ministers are threatening dire consequences for the Jisr al-Shughour deaths, which they blame (without offering evidence) on armed gangs. Their alarm is justified in one respect: this turmoil threatens the very existence of the Assad clan's ascendancy. Of the more than 1,000 civilians killed since the uprising began in March, the largest number – at least 418 according to a new Human Rights Watch report – died in the south-western Daraa governorate.

This week's events in Jisr al-Shughour, involving organised armed resistance and well-directed counter-attacks against regime targets, are of a different order of seriousness to Daraa's peaceful pro-democracy protests. In Daraa, the report says, "systematic killings and torture" by security forces probably amounted to crimes against humanity. So what untold horrors may be in store for Jisr al-Shughour residents, where the stakes are so much higher and where the same media curbs prevent independent scrutiny?

This chill moment is reminiscent of the day in July 1995 when Serbian forces brushed aside UN peacekeepers and seized the besieged Bosnian town of Srebrenica. Europe held its breath, fearing the worst. What transpired was even more awful than most could have imagined.

Assad should know by now that violence added to violence is not the answer. Amazingly, he does not. Or perhaps he is no longer in control, superseded in effect by his more martial younger brother, Maher, and other Alawite hardliners in the palace-general staff clique. The risk of civil war now looms large over Syria, in part because of this uncertainty about who is in charge; in part, also, because much of the Jisr al-Shughour bloodshed seems to have been the result of infighting between reluctant army units, filled with conscripts, and plainclothes security men – Syria's equivalent of Iran's notorious basij militia.

Wissam Tarif, director of Insan, a human rights organisation, was quoted on Monday as saying that many deaths resulted from clashes between loyalists and defectors, an account he said was backed up by local witnesses. There have been previous reports from other flashpoint towns of conscripts being shot for refusing to open fire on civilians, always officially denied. But the unprecedented regime casualty list in Jisr al-Shughour suggests the rot is spreading inside the many-headed security apparatus. Assad now faces two revolts. One on the streets, another within his own power structures. Like autocrats elsewhere, he will discover you cannot shoot down an idea.

By trying to externalise the conflict away from Syria's cities into the wider region, effectively projecting it on to Israel and potentially Lebanon and Iraq too, the regime poses a greater threat to western and Israeli interests than at any time since the 1973 Ramadan (Yom Kippur) war.

France and others are finally waking up to this evolution, with Paris demanding UN security council action. There is talk of referrals to the international criminal court. The US is considering even tougher sanctions. Assad's legitimacy "if not gone, [has] nearly run out", says Hillary Clinton. Nobody is talking about military measures, not yet at least. But momentum is building. Meanwhile William "behind-the-curve" Hague remains publicly fixated on his misjudged pursuit of Libya's Gaddafi and a Yemeni boatlift – all but oblivious to the vastly more dangerous implications of a Syrian implosion.

Recent incursions into the Israeli-occupied sectors of the Golan Heights, orchestrated by Damascus, dramatically illustrate how the Syrian conflagration could be purposefully spread. And what price a completed US withdrawal from Iraq this year if the country is destabilised by a spillover flood of Syrian combatants and refugees?

Southern Lebanon, ruled as a fiefdom by Iranian-armed Hezbollah, resembles an ideological hayfield scorched by five years of drought – while in Beirut the only certainty is political weakness. One match, struck in Damascus, might be all it needs to ignite a repeat of the July 2006 rocket war against northern Israel. And Israel, as ever, is not one to show restraint when brutal escalatory over-reaction will do.

Behind the expanding Syrian crisis lurks Iran. The Tehran regime is likewise embattled and destabilised by popular demands for reform, bitterly divided and seeking to deflect and project domestic unhappiness on to foreign foes. Two new developments this week amply illustrate the gathering danger.

One is the International Atomic Energy Agency's confirmation that buildings destroyed by Israeli bombers in 2007 housed an illicit Syrian nuclear reactor, most probably built in collaboration with Iran. Does Syria have other nuclear capabilities the IAEA does not know about? Nobody can say. Second, Iranian attack submarines have entered the Red Sea, the Fars news agency reported, accompanied by elements of the Iranian navy's 14th fleet. Their goal, it said, was to "collect information and identify other countries' combat vessels".

This is disingenuous – and alarming. Iran's goal is to project its military and political influence across a weak, restless Arab world. And to protect its repressive brother-in-arms, Syria, from western interference, military or otherwise. Iran's deluded, autocratic regime would rather fight than compromise on Arab spring democratic change. It may yet get its wish.