The assassination Tuesday of a senior Hezbollah commander in Beirut has heightened sectarian tensions in Lebanon, already aggravated by the civil war in neighboring Syria that has become the main battleground in a 1,400-year-old schism in Islam.

Assassinations in the Middle East are often hard to decipher because there are so many mutually antagonistic parties at each other's throats. There's never any shortage of suspects for -- or beneficiaries of -- a killing.

So it's hard to figure out who was behind the assassination of a man whose identity and position were known only to a few Hezbollah insiders, and what the objective of killing him might be.

Hassan al-Laqqis was believed one of the most important figures in Hezbollah, a powerful Shiite organization and Iran's key Arab ally. But he was barely known outside the movement's inner circle.

So when he was shot to death outside his apartment block -- even his neighbors had no idea he was a high-ranking Hezbollah official -- shortly after midnight by unidentified gunmen, it was clear there had been a massive and dangerous breach of Hezbollah security.

A day earlier, the party's secretary-general, Sheik Hassan Nasrallah, who is reputed to have survived at least one assassination attempt blamed on Israel, publicly accused Saudi Arabia's intelligence service of masterminding attacks by Sunni jihadists against the movement and its Shiite followers in recent weeks that killed or wounded scores of civilians.

Those attacks were a direct result of Hezbollah's intervention in the 32-month-old Syrian conflict to support President Bashar Assad, another Iranian ally, whose regime is dominated by minority Alawites, an offshoot of Shia Islam.

Saudi Arabia's Sunni monarchy, which is locked in an increasingly bitter confrontation with Shiite Iran for supremacy in the Persian Gulf and indeed in the wider Muslim world, is supporting rebel forces seeking to topple Assad.

Right now, that's Riyadh's top priority. But the confrontation is rooted in the religious schism that dates back to the death of the Prophet Mohammed, Islam's founder, in 632 A.D. and the struggle for control of the religion that followed.

Saudi Arabia's powerful foreign intelligence service, the General Intelligence Presidency, headed by Prince Bandar bin Sultan, is funding and arming some rebel forces in Syria.

Bandar, the former Saudi ambassador to the United States, has been involved in covert operations for decades and right now his key targets are Iran and Hezbollah.

Arab and Western intelligence sources say Saudi intelligence is conducting covert operations in Lebanon, a key conduit into Syria, and arming Lebanese Sunnis to fight Hezbollah.

Riyadh and Sunni leaders in Lebanon deny that. But the confrontation between Riyadh and Tehran sharpened dangerously after November's interim nuclear agreement between the U.S.-led Western powers and Iran.

The Saudis felt betrayed and weakened because Iran's nuclear program remained effectively intact. They apparently intensified the intelligence war with Iran and Hezbollah.

Hezbollah, with its best forces heavily engaged in a major regime offensive in Syria aimed at crushing Sunni bases along the Lebanese border, did not want to get dragged into a second front fighting Sunni militants in Lebanon.

It did not visibly respond to the bombings and rocket attacks.

That restraint continued even after the Iranian embassy in Beirut was hit Nov. 19 by two suicide bombers. Both were identified as Sunnis, one a Lebanese, the other a Palestinian living in a southern refugee camp known as a jihadist hotbed.

The attack was seen as a direct challenge to both Tehran and Hezbollah.

Publicly, Hezbollah has blamed Israel for killing al-Laqqis, who informed sources say headed Hezbollah's weapons procurement and development.

That would mean he operated closely with Iran's al-Quds Force, covert arm of the Revolutionary Guards Corps that supervises Hezbollah, and thus was a target for Israeli intelligence. (Israel denied involvement.)

The party says he'd survived several Israeli plots to kill him.

But he would also be a prime target for al-Qaida and its affiliates, and the Saudis, who have long run covert operations in Lebanon.

That said, the Israelis say they're facing more than 40,000 Hezbollah missile and rockets; so it must be presumed neither they nor Hezbollah, bogged down in Syria, are looking for a fight.

Right now, the betting is Sunni militants killed al-Laqqis, possibly seeking to provoke Hezbollah into a second front that would weaken the Assad regime at a critical time.