Lebanon blasts hit Iran's embassy in Beirut
"Saudis, and Jews," said a woman stumbling away from the bomb site, reciting the standard demonography of blame here in Shia south Beirut, after 22 people died and more than 140 were injured in an attack outside the Iranian embassy.
It is far more likely, however, that this attack was linked to Iran's support for the Syrian regime.
As he arrived at the scene, I asked the Hezbollah MP Nawar al-Sahili whether this was payback for what Iran was doing in Syria.
"It's a message," he said. "The [only] solution in Syria is a political solution. So who did this now doesn't want a political solution."
The attack was claimed by a Lebanese Sunni group which is part of al-Qaeda and fighting in Syria, the Abdullah Azzam Brigades.
Whether or not that claim turns out to be true, the Syrian rebels are suffering - and they blame Iran, along with its Lebanese ally, Hezbollah.
Just over the border, the Syrian regime is successfully prosecuting an offensive designed to cut off the rebels' supply routes from Lebanon. The result can be seen in new groups of refugees trudging despondently into the border town of Arsal.
Help from Iran - and Hezbollah - could be the decisive factor if the rebels are chased out of their last remaining strongholds along Syria's border with Lebanon. A number of Syrian rebel groups have vowed revenge.
Syria is a proxy war, the Iranians backing the regime, Saudi Arabia backing many of the rebel groups.
"Stay away from anything Saudi in Lebanon," wrote a Lebanese journalist about the expected next upward ratchet in the spiral of violence.'Let them face us'
If further violence is directed against a Saudi or Saudi-linked target, it would be political rather than purely sectarian. But of course there is a sectarian aspect to all of this. The communal divisions in the Syrian conflict are mirrored over the border in Lebanon.
"These people won't fight us face to face," said a Shia man whose head was bandaged from an injury received in the bombing.
"So they use suicide bombers. Let them face us. We're ready for them."
Such talk is why the streets of Beirut are noticeably more tense tonight. Young Shia men wearing masks and riding motorbikes have been riding out in packs into some neighbourhoods in a show of strength.
The last time something like this happened, 27 people died in a bombing in Shia southern Beirut. Eight days later, the response came, a bombing outside a Sunni mosque in Tripoli that killed 42 people.
So it is not the first time that the civil war in Syria appears to have reached over the border to cause mayhem here in Lebanon. It is not the first time, either, that there's been an attack in Shia south Beirut.
But everyone in Lebanon knows that an attack on an Iranian target is something different. Everyone is waiting and watching anxiously to see what the consequences of such an attack might be.