The deadly twin suicide bomb attack Tuesday against the Iranian embassy in Beirut illustrates how the conflict ravaging neighboring Syria is becoming more sharply defined as a Sunni-Shiite struggle between regional powerhouses Saudi Arabia and Iran.
Iran is a staunch backer of the regime of Syrian President Bashar al-Assad, providing logistical support and training. With that help, and a few thousand fighters from Lebanon's Iran-backed Shiite militant group Hezbollah, the Syrian Army has clawed back some rebel-held territory in recent weeks.
Saudi Arabia, on the other hand, is a champion of the mainly Sunni armed opposition in Syria, a role it reportedly intends to pursue more forcefully in the coming months.
The bomb attack, which killed 23 people, was not the first to hit the mainly Shiite-populated southern suburbs of Beirut this year. Two car bomb attacks in July and August left a total of 27 people dead and nearly 400 wounded. But today's attack featured new tactics and was the first against a strategic target, which suggests that more pre-planning went into it than with two previous random car bombings.
It also came amid indications that a long-anticipated regime offensive against the rebel-held Qalamoun region between Damascus and Homs is under way, which is expected to trigger a violent backlash in Lebanon.
The first bomb consisted of some 4.4 pounds of explosive transported by a suicide bomber riding a motorcycle who detonated the device beside the gates to the Iranian embassy. The second bomber drove a vehicle laden with an estimated 110 pounds of explosive that blew up just outside the entrance to the embassy two minutes later.
The tactic was similar to attacks attributed to Al Qaeda in Afghanistan, Iraq, Yemen, and Pakistan, but it was the first time that suicide bombers have appeared in Lebanon since the onset of the crisis in Syria in March 2011.
The Al Qaeda-linked Abdullah al-Azzam Brigades claimed responsibility for the bombings, although the claim could not be verified. The group previously claimed responsibility for a roadside bomb attack against a suspected Hezbollah vehicle in the Bekaa Valley in July, which left one member of the party dead, and a rocket attack into Israel in August.
Sources close to Hezbollah in southern Beirut said that the party's cadres blamed Saudi Arabia for the embassy bombing and demanded revenge.
“They are saying the only acceptable retaliation is to bomb the Saudi Embassy [in Beirut],” said one resident.
Ali Mikdad, a Hezbollah lawmaker, delivered a stern warning to the perpetrators of the embassy bombing.
“We got the message and we know who sent it and we know how to retaliate,” he told Lebanon's Al Mayadeen TV channel.
Saudi officials recently voiced displeasure with US policies toward Syria and hinted that they would pursue a more robust policy toward the Syrian conflict independent of Washington. Saudi Arabia was particularly furious at Washington's decision in September to drop a planned series of air strikes against the Syrian military in response to the Assad regime's alleged use of chemical weapons against rebel areas of Damascus in August.
The campaign of air strikes was abandoned after the US and Russia brokered a deal in which Syria agreed to give up its arsenal of chemical weapons.
A Saudi source close to the Kingdom's leadership said that Riyadh cannot afford to let Iran “win” in Syria by saving the Assad regime and defeating the armed opposition. The source added that the Saudis were determined to “defeat” Iran and would more fully back rebel forces.
Lebanon is deeply divided over the conflict in Syria and has felt the violent blowback of the war. According to diplomatic sources in Beirut as well as Arab intelligence sources, Syrian Sunni militants and their Lebanese allies are stockpiling weapons and explosives across Lebanon in anticipation of using them against Shiite-populated and Hezbollah-controlled areas.
Some militant cells have been caught and arrested by the Lebanese authorities. The potential trigger is the campaign to drive rebel forces from the strategically located and mountainous Qalamoun area, adjacent to the Lebanese border.
Last week, the Syrian military launched an attack against Qara, a town at the northern end of Qalamoun, which led to some 8,000 Syrians fleeing across the border into Lebanon. The Syrian Army reportedly seized the town, which leaves them well-placed to move against rebel areas further south.
Hezbollah is expected to play a lead role in the Qalamoun offensive. A Hezbollah fighter who recently returned from a tour in the southern Damascus front says that the campaign for Qalamoun would last many months and would resemble a counter-insurgency campaign using Hezbollah, air power and artillery.
The regional implications of the battle for Qalamoun were clear to him.
“This is a battle between Qassem Suleimani and Bandar bin Sultan,” he joked, referring respectively to the head of the Iranian Revolutionary Guard's elite Quds Force, who is believed to be playing a key role in Syria on behalf of the Assad regime, and the head of Saudi intelligence, who is the architect of Riyadh's reinvigorated posture toward Syria.