Syria is undoubtedly the country in which the Arab spring has the most profound geostrategic implications. The fall of Bashar al-Assad's government would change the situation in the Middle East entirely. Indeed, even the impasse that appears to prevail today has accentuated the polarisation of regional actors, between those who are for Assad and those who are against him, with the risk that any internal escalation in Syria will have wider repercussions. As for the western powers, they are out of the game for the moment. The Libyan adventure makes intervention almost impossible. Nato doesn't have the resources to act and a US intervention on the scale that would be required is highly unlikely, even though the stakes in Syria are infinitely higher than they are in Libya.

The novelty - and the great danger - is that the Syrian crisis brings into conflict two states that, until now, have coexisted peacefully despite belonging to opposing camps, namely Iran and Turkey. Both are directly implicated in what is happening in the country.

Turkey is involved not as a member of Nato, but in its new role as a major regional power. For the Iranians, the fall of the regime in Damascus would be a catastrophe. Syria is Iran's only Arab ally and a vital link with Hezbollah in Lebanon, which is the spearhead of Iranian influence in the Middle East. Without Syria, Iran's foreign policy in the region - in which it positions itself as the last remaining bulwark against Israel and as the defender of an Arab nationalism betrayed by the regimes (and, although this is not said explicitly, abandoned by the new democratic movements) - would fall apart. Were Assad's clan to be ousted, the replacement would be Sunni and anti-Iranian, whatever its other political affinities. For this reason, Iran has sent money, military advisers and arms to Syria. And it would not hesitate to go further in order to save Hezbollah.

Behind red lines

The Turkish position is harder to read. It has moved from compliance to a hostility that stops just short of intervention. Turkey is amassing troops on the Syrian border, trying to organise Syria's internal opposition and calling overtly for the overthrow of the regime. This stance is unprecedented in the history of the modern Turkish state - until now, it has used military force in the Middle East only when dealing with the intermittent threat of the Kurdistan Workers' Party (PKK). It has never called for regime change - not even when the Islamic Republic of Iran openly contested the legitimacy of Kemalism. Not only has it never sent troops into the Middle East (one recalls Turkey's refusal to enter Iraq in 2003, despite a request from the US to do so), but it has not allowed its territory to be used as a base for any Middle Eastern opposition movement. And with good reason: as long as it was preoccupied with entry into the European Union, Turkey remained very prudent where the Middle East was concerned. Today, however, its proactive foreign policy compels it to take sides in local conflicts even if it would prefer to play the role of mediator.

A dangerous and unexpected scenario looms: a confrontation, through intermediaries, between Iran and Turkey, while the usual arbiters, Israel and the US, keep their powder dry. The Syrian regime represents all that Israel detests, but it has always respected "red lines". Syria is an adversary but one that can be managed. Unless Iranian troops set foot on Syrian soil, it is highly improbable that the Israelis will act.

While this mobilisation takes place on Syria's borders, it is hard to identify the political forces at work in the country. Beyond the knowledge that the regime is primarily the mouthpiece of an Alawite minority, even if it has some support among Sunnis, we can be sure of very little. How united are the Alawites? What role is the Muslim Brotherhood (MB) playing in opposition? Even the local population seems to be largely in the dark: everyone fears a civil war, but at the same time denies the reality of sectarian tensions today. It is clear that Assad is playing on this fear of sectarian conflict; he reminds the Sunnis of the Hama massacre in 1982 and the Alawites that power can only be maintained through force. To the Christians, the regime appears to be the best protection against the kind of anti-Christian violence that erupted in Iraq after the invasion in 2003.

Choosing sides

What of the Kurds (who number well over a million)? The borders with Turkey and Iraq are open and arms are passing back and forth. The PKK has a presence in Syria and the Kurds are taking against a regime that has marginalised them. In this, they join with the Sunni majority against the government.

The MB no doubt failed to construct a clandestine activist network after the repression of 1982-83. Yet the policies that were designed to counter the MB have had perverse effects - they have given carte blanche to Sunni religious conservatives who, although they appear to be apolitical, regard the Alawites as heretics and believe that Shia Iran has no business in Syria. Where are they going to stand? In my view, against the regime.

The Syrian internal situation will continue to escalate, causing a further rise in tensions between Turkey and Iran. And all this at a time when no one really knows how the political forces inside Syria are distributed and when there is no precedent for the confrontation between Ankara and Tehran - and thus no guide for preventing the situation from spiralling out of control.

Translated by Jonathan Derbyshire

Olivier Roy is professor of social and political theory at the European University Institute in Florence. His books include "The Failure
of Political Islam" (I B Tauris, £15.99) and “Holy Ignorance: When Religion and Culture Part Ways" (C Hurst & Co, £20)