Mohamad Chatah was a Sunni member of the Lebanese parliament closely affiliated with the Saudi-backed Future Movement party, led by billionaire and former Lebanese prime minister (2009-11) Saad Hariri, who took over the helm after the assassination of his father, former prime minister Rafiq Hariri, in 2005. He was a staunch critic of the Shiite-aligned minority Alawite-dominated regime of Syrian President Bashar al-Assad and the Lebanese Shiite Hezbollah. As such, he was also critical of Iran's Shiite Islamic regime for supporting the last two.

His killing, blamed on Hezbollah, came after a spate of assassinations of a few prominent Lebanese Sunni and Shiite leaders, and the bombing of the Iranian embassy in Beirut in the past few months.

Although Lebanon has increasingly been drawn into the Syrian crisis since it began nearly three years ago, and the Sunni-Shiite divide has troubled the region for a long time, both have reached a feverish and alarming level. The Sunnis and Shiite are pitched against one another not only in Lebanon and Syria, Iraq and Bahrain, but also across the Middle East, with a spillover effect on the wider Muslim world, from Pakistan to Indonesia and Malaysia.

It has made Saudi Arabia, which claims the leadership of Sunni Islam, and Iran, which champions the cause of Shiite Islam, lock horns in a number of proxy conflicts. Tehran has backed Hezbollah and the Assad regime as well as some powerful Shiite groups in Iraq, which the US occupied from 2003 to 2011 but failed to turn into a bastion for an American-type democracy, and opposed the Sunni Arab minority rule in Bahrain. Riyadh has actively sought to counter Iran in all these places and beyond.

In conjunction with some of its conservative oil-rich Arab partners in the Gulf Co-operation Council, it has denounced Hezbollah as a ''terrorist organisation'' and has intimately supported Hariri's party and its affiliates. It has also backed the Syrian opposition forces to the Assad regime and grown highly critical of the US for failing to act militarily to expedite the demise of the regime. In the case of Iraq, it has thrown its weight behind the country's Sunni minority vis-a-vis its Shiite majority, and in relation to Bahrain, it has sent troops to defend its monarchy.

Meanwhile, although officially welcoming Iran's interim agreement with world powers, most importantly the US, over its nuclear program in November, Riyadh has done so with a great deal of trepidation. It has just announced $3 billion in military assistance to the Lebanese government to fight terrorism - a reference to Hezbollah. The cycle of mutual recrimination emanating from Saudi and Iranian sources has increasingly become vicious, with both sides also watching and marginalising their Shiite and Sunni minorities.

The ironic aspect of the whole development is that this is more in pursuit of conflicting geopolitical interests rather than occasioned by serious religious differences. The Shiite-Sunni schism dates from a dispute over the leadership (Khalifa) of the Muslim community (umma) following the death of Prophet Muhammad in 632. Those who supported the Prophet's cousin and son-in-law, Ali ibn Talib, as the rightful leader (caliph), became known as the Shi'atu Ali (''the party of Ali''; later, the Shiite).

The Shiites held that only Ali and his direct descendants (imams) could be the rightful leaders of the ummah. The majority, on the other hand, who favoured the succession of the Prophet's societal leadership by his four companions in the order of seniority, with Ali coming last, rejected the notion of birthright and insisted that the caliph be elected by the umma itself. Those who held this opinion became known as the ‘‘people of the tradition’’ (sunna), or Sunnis.

The dispute over who should have rightfully succeeded the Prophet’s leadership came to spawn a number of dogmatic and cultural traditions and practices between the two sects, setting them apart as two sectarian communities. Complicating their relations has also been the fact that they encompass a large number of sub-groups, each with outward characteristics of their own.

However, on the whole, when it comes to the fundamentals of Islam – belief in one God, Muhammad as the Prophet of God and the Koran as the words of God – they share a lot in common. Their differences have surfaced sharply in history when they are deployed for geopolitical objectives. In modern times, this has never been as prominent as now, especially since the Iranian revolution almost 35 years ago. The overthrow of the Shah’s pro-Western regime and its replacement with Ayatollah Khomeini’s Shiite Islamic government and the latter’s initial efforts to export its brand of Shiite revolutionary Islam to the predominantly Sunni Muslim region brought sectarianism sharply into political and strategic focus.

The time has come for the Iranian and Saudi leaderships to settle their geopolitical differences peacefully through diplomatic means rather than sectarian guises. With the recent election of the moderate-reformist Islamist Iranian President Hassan Rouhani, there is now an important opportunity for dialogue and co-operation. Rouhani has extended a hand for better relations with Saudi Arabia in particular, and Sunni Muslims, who constitute some 90 per cent of the 1.5 billion Muslims in the world, in general. Alternatively, the use of sectarianism as a political tool carries a serious risk of causing the Muslim world to consume itself from within rather than being demolished by an outside power.

Amin Saikal is professor of political science and director of the Centre for Arab and Islamic Studies (the Middle East and Central Asia) at the Australian National University, and the author of forthcoming book Zone of Crisis: Afghanistan, Pakistan, Iran and Iraq.