There's more riding on a U.S. reconciliation with Iran than just convincing Tehran to scale back its murky and widely feared nuclear program, analysts say.

An accord with Tehran could do a lot to ease the swelling conflict between the Muslim world's mainstream Sunni sect, led by Saudi Arabia, and the breakaway Shiites led by Iran, that's become the central issue in the bloodletting in Syria, Iraq and Lebanon and threatens the stability of the entire Middle East.

The religious rift dates back to the dynastic dispute triggered by the death of the Prophet Muhammad in 632 A.D.

Quiescent for centuries, it has flared into violence in recent years, particularly with the turbulent birth of the radical Islamic Republic of Iran in 1979.

This new confrontation in a dispute that goes back 14 centuries has come to define the modern-day rivalry between Saudi Arabia, which as the birthplace of Islam and guardian of its holiest shrines, considers itself the heart of the Islamic world, and the upstart Islamic Republic, for dominance of the region.

The growing sectarianism that now marks the 30-month-old civil war in Syria and the worsening slaughter in Iraq is spilling over into Lebanon, threatening to ignite a new civil war, this time between the Sunni extremists of al Qaida and the Shiite warriors of Lebanon's Hezbollah.

The Syrian war is the first conflict that has thrust al Qaida and Hezbollah, Iran's highly prized Arab ally Lebanese, into direct conflict.

At least one U.S. commentator has suggested these two religion- and ideology-driven protagonists be left alone to savage each other, allowing the Americans to get rid of two of its relentless tormentors.

Constraining Iran's nuclear ambitions is the declared primary objective of the negotiations between the Western powers and Iran, which is also the principal backer of Syria's embattled President Bashar Assad.

But as international affairs commentator David Gardner observes, "two other prizes such a deal could unlock are enlisting Iran's help in addressing the most unmanageable conflicts of the Middle East, and starting to turn back the tide of sectarian poison coursing through the region...

"Detente with Iran could eventually persuade Tehran to elbow aside the Assads -- now almost totally dependent for their survival on the Islamic Republic -- and unlock a transition out of Syria's misery.

"But getting Iran inside the diplomatic tent could also make it easier to manage, if not resolve, a host of other regional problems," such as the increasingly sectarian bloodletting in Iraq and Lebanon, observed the Beirut-based Gardner.

"Lebanon and Iraq are in practice becoming part of the Syrian battlefield. First Lebanon, then Iraq and now Syria have all been convulsed by sectarian civil war.

"But what has been a Sunni-Shia subplot in the region's drama burst onto center stage after the U.S.-led invasion of Iraq in 2003," he said.

"That put the Shia minority within Islam -- a majority in Iraq -- in power in a major Arab country for the first time in nearly a millennium, tilting the regional balance of power toward Iran, and igniting a sectarian bloodbath...

"This is a primordial struggle within the Muslim world. Any attempt to stabilize the Middle East and its myriad conflicts needs to search for the taps of sectarian poison and turn them off," Gardner said.

"A deal with Iran would be a start. It would have to be followed by a sit-down with Saudi Arabia, to discuss the extremist and sectarian ideology it exports along with the oil it sends to the world."

The religious schism in Islam stemmed from a dispute over who would succeed the Prophet. The dividing line became more indelibly defined in the 16th century when Persia's Safavid rulers made Shia Islam the state religion, while Arab lands followed the more mainstream Sunni Ottomans .

The Safavids fought the Ottomans and sought to purge Iran of Sunni influence.

"Religious affiliation became amalgamated with ethnic identity ... that deepened religious differences," Persian Gulf analyst Hassan Hassan (desk: Hassan Hassan is correct) observed.

"This tendency is virulent today and fuels divisions between Arabs and Iranians and, by extension, between Arab Shiites and Sunnis...

"Rising sectarian sentiments, arguably the worst in a century, are being stoked by extremists on both sides and exploited for political ends," Hassan warned.