Nine days ago the influential Sunni cleric Yusuf al-Qaradawi denounced the Lebanese Shia Hezbollah movement – whose fighters helped Bashar al-Assad's regime retake the Syrian city of Qusair last week – as the "party of Satan".
Speaking in Doha not long before Qusair's fall, Qaradawi did not stop there: the cleric, whose speeches and sermons are heard by millions, went a dangerous step further, calling on Sunni Muslims with military training to support the Syrian uprising against Assad.
It was a sermon that not only marked a sharp shift in the sectarian tensions in the Middle East between Sunni and Shia but an escalation in Qaradawi's own rhetoric. When I heard him preach on Syria at Cairo's crowded al-Azhar mosque last autumn, he was sharp in his condemnation of the Assad regime, but stopped short of endorsing a jihad.
In Doha, however, Qaradawi's remarks embraced a more dangerous sectarian notion. "The leader of the party of the Satan comes to fight the Sunnis … now we know what the Iranians want … they want continued massacres to kill Sunnis," Qaradawi said. "How could 100 million Shias defeat 1.7 billion [Sunnis]? Only because [Sunni] Muslims are weak."
Qaradawi's comments – endorsed last week by Saudi Arabia's grand mufti, Abdul Aziz al-Asheikh – did not come out of nowhere. They were a direct response to a speech made by Hezbollah's general secretary, Hassan Nasrallah, in Beirut, not only admitting that his fighters were in Syria but pledging that his men would help Assad – a member of the Shia Alawite sect – to final "victory".
If ever evidence was needed of the escalating sectarian dimension to the growing regional instability in the Middle East – in which the worsening conflict in Syria is playing a large part – it was visible last week.
It is visible in the rubble of Syria's Qusair, emptied now of much of its population, and taken by a joint force of Hezbollah and Assad government forces, as well as in Lebanon's seaside city of Tripoli, the country's second largest, where gun battles between Alawites and Sunni militias are continuing.
It has been visible, too, in Iraq, where lethal tensions, in part inspired by Syria but more largely by the country's own political tensions, have been growing almost by the week, witnessing more than 1,000 deaths in May, the highest monthly toll since 2008.
And it has been Syria – above all – that has acted as a magnet for those looking to fight, for both Sunni jihadis and for Iraqi and Lebanese Shias alike.
It has become a cliche in recent months to talk of an inevitable and intractable sectarian divide between Sunni and Shia, over a schism in Islam that occurred 1,400 years ago. The reality is that the present rising tensions in the Middle East are far more complex than simple religious hatred. Rather, they reflect a growing friction rooted in more recent competitions over power, rights and identity which have been exacerbated both by the war in Iraq and by the reconfigurations of the Arab spring.
At the very heart of the debate is how much sectarian tensions themselves are driving the new conflicts or whether Sunni-Shia tensions have been co-opted into local and regional competitions whose nature is as much about power, politics and the distribution of resources as it is religious.
The split in the two branches of Islam is almost as old as Islam itself, resulting from a political struggle for leadership between followers of the Prophet Muhammad after his death. What emerged were sometimes subtly different – and sometimes quite radically different – interpretations of Muhammad's teachings. Despite that, there has been no equivalent in Islamic history of the Thirty Years' War that pitted Protestant against Catholic in Europe, while for long periods and in many places – not least Iraq despite its recent problems – Shia and Sunni have not only coexisted but widely intermarried.
Marc Lynch, director of the Institute for Middle East Studies at George Washington University, writing recently in Foreign Policy, cautioned that the narrow emphasis on sectarianism was unhelpful. "The sectarian master narrative," wrote Lynch, "obscures rather than reveals the most important lines of conflict in the emerging Middle East. The coming era will be defined by competition between (mostly Sunni) domestic contenders for power in radically uncertain transitional countries, and (mostly Sunni) pretenders to the mantle of regional Arab leadership. Anti-Shia-ism no more guarantees Sunni unity than pan-Arabism delivered Arab unity in the 1950s." In other words, the emerging conflicts are largely inter-Sunni rather that Sunni-Shia. Lynch also points to the rivalry between Qatar and Saudi Arabia to arm different rebel factions, a competition, he suggests, that has undermined Syrian opposition unity.
Geneive Abdo, a fellow at the Stimson Centre thinktank and author of The New Sectarianism, however, admits to being "fairly pessimistic" about the current trajectory of Sunni-Shia tensions, arguing that it comes amid a wider "intensification" of sectarian identity across the Middle East that cannot be explained easily with reference to social, economic or political context.
"One mustn't forget that some of the new sectarianism began with Iraq [following the invasion]. The fall of the authoritarian regimes during the Arab spring," she adds, "coincided with an increased interest in identity politics of all kinds, including sectarian identity."
Abdo – like a number of other analysts – traces the roots of the present Shia-Sunni tensions back to the 1960s and 1970s, rather than further back in time. That period saw the beginning of the Shia revival movement in Lebanon which – like the opposition movement in Syria today – argued for equality and inclusive rights for Shias in Sunni-ruled states.
Abdo believes, however, that the new sectarianism is being driven by competing factors, including both the way in which Sunni and Shia states are engaged in Syria, sectarian tensions in Syria itself and "the perception" in places such as Bahrain, where a Sunni monarchy is in competition with a Shia majority over political rights, that the competition is sectarian in nature – a self-fulfilling prophecy.
The issue of how sectarianism is playing in the region's emerging conflicts – not least in Syria – is made doubly difficult by the fact that the spectre of widening Sunni-Shia conflict is also being cynically exploited, a claim made by the Iraqi scholar Harith al-Qarawee, writing in National Interest earlier this year about Iraq.
There, he argues, "sectarian identities are used by political entrepreneurs to achieve political goals. Although cultural symbolism and collective narratives are a part of this process, the real objectives are political – and largely calculated."
Qarawee and others also point to a recent process of "Sunnification". On a local level in Iraq, this has seen minority Sunnis – who once dominated the country and have been politically and economically excluded in a Shia-dominated post-Saddam Iraq – increasingly embrace a sectarian identity.
More widely, if much less dangerously, that has coincided with the emergence of new Islamist governments across the region closely associated or dominated by the Muslim Brotherhood.
Others argue that the sense of a sectarian crisis – most notably over Syria – has been confected by the Assad regime.
"The sectarian element was introduced into the revolution in March 2011 by the Assad regime itself, which wants to identify it with sectarian strife," says Syrian writer and analyst Rime Allaf. "It deliberately embraced this idea because it knows people are afraid of it … The regime and its allies in Hezbollah have tried to present their position as a defensive one, but people are not buying it." She argues, too, that Assad's recent co-option of Hezbollah is as much to do with his lack of trust in sections of his own armed forces as a pan-regional strategic alliance spreading from Iran to Lebanon.
And if it has been Hezbollah's overt intervention in the fighting in Qusair that has set the alarm bells ringing ever more loudly, it is worth noting that the Hezbollah's interest in Syria has less to do with the fate of its Alawite co-religionists and everything to do with its own survival and interests.
A Lebanese client of Iran, Hezbollah has long relied on the Assad regime as a conduit for the sophisticated arms and other support that has allowed the movement to exert a disproportionate influence in Lebanon.
It has not only been in Syria where the alleged danger of sectarian interference has been used to justify human rights abuses. In Bahrain, which has seen intermittent protests for two years and a continuing crackdown by Sunni rulers on marginalised Shias, the ruling family has tried to paint legitimate protests as Iranian-inspired interference.
Vali Nasr, a member of the US state department's foreign policy board and author of The Shia Revival, who has charted the increasing importance of Shia influence and politics since the fall of Saddam, suspects there may be more subtle doctrinal considerations as well at work in the increasingly febrile comments of those like Qaradawi. Nasr points to Qaradawi's remark that Sunnis can only be beaten if "they are weak".
"Hezbollah and Iran pulled something big off. They showed [over Qusair] that they are more capable of fighting than Sunnis. For those like Qaradawi – for whom the discourse is about empowerment for followers of the true religion – it cannot be allowed that Sunnis are shown as somehow feeble."
While Nasr has long predicted a decisive shift in the centre of gravity in the Middle East towards Shia Iraq and Iran, he is careful to distinguish between the motivations of individual Shia fighters who are being drawn to Syria from places like Iraq, and Sunni jihadis who have travelled to fight for Sunni jihadi groups like Jabhat al-Nusra, following recent claims of the new emergence of a kind of "Shia jihadism".
"For Shias, Syria is not the Spanish civil war or Afghanistan. Many of those Shia who are going to fight are going from places like Lebanon and Iraq because they believe they are fighting for themselves.
"It is seen as a forward deployment by those who fear that, if Assad loses, Sunnis will come after them. They see it as a pre-emptive defence." He adds: "People in the wider Middle East care about Syria not because they necessarily care about Syrians but because they care about their own fights."
Nasr, who is more optimistic than most, suggests, too, that the current tensions can be seen as marking the final unravelling of the shape of the region first conceived in the Anglo-French Sykes-Picot agreement that foresaw the dismemberment of the Ottoman Turkish empire.
"Those structures are now coming undone: first under the boots of US soldiers in Iraq and more recently under the heels of the democracy protesters of the Arab spring."