As the Syrian crisis worsens, if you thought that things in the Middle East were already complicated and unstable enough, then the attack on an Israeli tourist bus in Bulgaria has just made things that much worse.

Israeli security experts believe that this is just the latest - and the first successful - attack in a series of operations against Israeli targets around the world, planned by the overseas operational arm of the Lebanese group Hezbollah.

And behind Hezbollah the Israelis see the hand of Iran; an Iran smarting at a series of attacks against its nuclear scientists, widely believed to have been planned, maybe even carried out, by the Israelis.

For its part Hezbollah insists that it had nothing to do with the Bulgarian attack.

But a series of arrests - most recently in Cyprus - have given credence to Israel´s claims of a long-running Hezbollah plan to attack soft Israeli targets abroad.

The Burgas attack has potentially brought Israel into the frame of a crisis in which, up until now, it has been a concerned bystander.

Indeed, the Burgas attack has the potential to exacerbate three over- lapping crises - the long-standing tensions between Israel and Hezbollah in southern Lebanon; the growing chaos in Syria; and the wider struggle between Israel and Iran focussed on Tehran´s nuclear programme.

The stakes are high. A new regional conflagration beckons if any of the actors make a wrong move.

Israel has been watching events unfold in Syria with alarm, perhaps tinged with just a small measure of optimism.

The demise of the Assad regime - Iran´s principal Arab ally - would be a major blow to Tehran.

It would greatly constrain Iran´s regional ambitions.

But on the other hand, the Assad regime - father and son - have been known quantities. Israel´s border with Syria on the Golan Heights has been its quietest frontier since the 1973 war.

The collapse of Syria into sectarian chaos - chaos that could well spread to Lebanon as well - is worrying Israeli political leaders and military commanders.

There have already been murmurings of concern at Syrian troop levels in the Golan being reduced as the regime pulls reinforcements into the centre of the country.

Israel fears it could have an ungoverned space on its northern border akin to the growing security challenges posed by the breakdown of order in Egypt´s Sinai peninsula.

Add to this the fear of Syrian weapons - missiles and even chemical weapons - potentially falling into the hands of Hezbollah and it is no wonder Israeli military planners are uneasy.

Israel and Hezbollah in Lebanon have contrived an uneasy informal truce since Israel´s last major incursion into the country in 2010.

This operation was not a success for the Israeli military. Hezbollah emerged battered but with its confidence enhanced. Since then it has dramatically built-up its ground-to-ground missile force. Israel too believes that it has learned the lessons from its last military operation in Lebanon. Both sides are preparing for the next round in their struggle.

What links both the Syrian regime and Hezbollah in Lebanon - quite apart from their own close ties - is the patronage and support they both get from Iran.

Of course Israel regards Iran´s nuclear programme as a potential existential threat. It has trained and planned for an attack against Iran´s nuclear facilities. US pressure - not least the imminence of a US presidential election - tougher economic sanctions, and renewed efforts by the major players in the UN Security Council along with Germany to engage Tehran in negotiations have forestalled an Israeli attack up to now.

But three rounds of talks have not made any significant progress. Israel is fast losing patience and Israel´s own domestic political circumstances may come into play.

After the Kadima party quit the coalition a general election may be in the offing; perhaps in early 2013. Could this be a factor in determining the timing of a potential Israeli attack against Iran?

Of course such an attack could have dramatic consequences across the region. The Burgas attack has thus added a new level of complexity to an already difficult strategic picture.

Israel will no doubt respond against Hezbollah; but maybe not now. It already has bigger strategic threats to worry about. (© BBC MMXII 07/19/12)