The U.S. and most Western countries, notably Britain and France, are pointing the finger at Assad for the attack, while the Syrian government and its main international ally, Russia, blame the rebels.
At this point, except for those responsible, no one knows for sure who was behind the attack, or even what kind of chemicals might have been used.
UN weapons inspectors are now on the scene trying to determine whether chemical weapons were, indeed, used.
The international group Doctors without Borders, the source for the casualty figures, says, it "can neither scientifically confirm the cause of these symptoms nor establish who is responsible for the attack."
Its information comes from three hospitals in Damascus that "received approximately 3,600 patients displaying neurotoxic symptoms" on the morning of Aug. 21. MSF staff were not at the facilities themselves.
If that attack a week ago can be confirmed as a deliberate use of chemical weapons on civilians, it would go down in history as only the second such large-scale incident against civilians in modern times. (Though there have been allegations of at least five other uses of chemical weapons that have affected civilians in the two-year-old Syrian conflict, the first in March of this year.)
The first incident, a quarter century ago, is now nearly forgotten, but in both its similarities and its stark contrasts with the current situation, it helps with understanding the dilemma the world faces today.
The date was March 16, 1988, in a Kurdish town in Iraq, 14 kilometres from the border with Iran. The bloody Iran-Iraq war was in its eighth and final year.
One day earlier, the townspeople had liberated Halabja. Iraqi forces were abandoning the area and Iranian troops, guided by allied Kurdish guerillas, had briefly entered the town.
On March 16, according to eye-witness accounts and Iraqi pilots years later, poison gas was dropped from aircraft, killing several thousand civilians in the town, with the precise death toll unknown.
1988 poison gas attack killed thousands
Iran and Kurdish leaders, especially Jalal Talabani, now Iraq's president, alerted the outside world. Iran flew in journalists, whose images of streets littered with corpses were shown on newscasts. However, no independent investigators visited the area.
Claims by Iran and the Iraqi Kurds that Saddam Hussein's forces had carried out the gas attack were initially accepted. But on March 23, U.S. State Department spokesman Charles Redman said that "Iran may also have used chemical artillery shells in this fighting."
Other unnamed U.S. government officials, speaking to journalists off the record, also suggested that Iran, America's primary Middle East antagonist at the time, was responsible, at least in part.
"With the weight of the U.S. government behind it, this version soon proliferated, becoming a respectable interpretation of events ... framing the policy debate," writes Joost Hiltermann in his 2007 book, A Poisonous Affair: America, Iraq and the gassing of Halabja.
The book is the definitive account of what happened, and Hiltermann concluded it was Iraq, and only Iraq, that used chemical weapons against the people of Halabja.
It would take two years for the dominant, U.S. government view to shift from publicly blaming Iran to blaming Iraq, and that was only after Saddam hinted at undertaking a chemical gas attack against Israel. His ill-conceived invasion of Kuwait a few months later sealed the deal.
U.S. blocks response to attack
In 1988, the U.S. was allied with Iraq, and was providing order of battle data about Iranian forces to the Iraqis, while turning a blind eye to what it knew were chemical attacks against Iranian troops, a serious and flagrant violation of international law.
"It was the only slightly better of two bad choices: stop helping the Iraqis and the Iranians would likely win the war, or continue to work with a country now using nerve agents on the battlefield," writes Rick Francona this week on his blog. Francona was U.S. military liaison officer to the Iraqi forces in 1988.
Francona claims that the U.S. didn't yet know that Saddam had ordered the chemical attack on Halabja, but he is now adamant that it was Iraq that perpetrated that atrocity.
However, there are still many people who believe the old U.S. argument, and the debate continues in some circles about what exactly killed, sickened and maimed the townspeople of Halabja.
Fast forward 25 years, and the conflicting accounts from the Russians, Americans, Europeans as well as the Assad regime and the rebels, not to mention the lack of evidence to date, suggests it may take time to find out what really happened in Syria.
Halabja 'similar' to attack in Damascus
Stephen Pelletiere was with the CIA until 1988, before going on to teach at the U.S. Army War College in Pennsylvania, retiring in 2000 as a senior professor. He has written six books on Iraq and is working on another one about Halabja.
Pelletiere has been and continues to be one of the leading voices for the narrative that blames Iran for that chemical gas attack.
But he was also a high-level skeptic about the rationale for going to war with Iraq in 2003, and sees something similar taking place with regard to Syria today.
"If you look at the events surrounding not just Halabja but the whole fuss in the U.S. over going to war with Iraq [in 2003], and then you look at what's going on now in Syria, it follows an almost exact same pattern."
As he told CBC News, in 1988 there was every reason in the world why the Iraqi commander might have used gas but in the case of Syria, there's no reason at all."
For Pelletiere, it's illogical for Assad to resort to poison gas when UN inspectors had just arrived in Damascus and when his forces seemed to be gaining the upper hand in the war. "The logic is all on the side of a provocation," he argues.
Of course, the rest of the world doesn't know what Assad's logic might be in a situation like this, with rebel forces almost literally on his Damascus doorstep. But there is the possibility, at least, that chemistry might help sort the situation out.
Mathew Meselson, who heads the Harvard University program on chemical and biological weapons, looks at the science of these situations and notes we haven't seen any yet in the case of Syria.
"It's essential that any head of state or government official who's making momentous decisions on the basis of chemical analysis must talk not just with other political figures or subordinates, but with individuals who are deeply knowledgeable about the science itself," he told Bloomberg News.
He cited the case of U.S. allegations against the former Soviet Union in 1981, that it had supplied chemical agents to communist forces in Vietnam and Laos that turned out to be honeybee droppings.
U. S. Secretary of State John Kerry, who seems convinced that chemical weapons were used last week, was blunt yesterday: "All peoples and all nations who believe in the cause of our common humanity must stand up to assure that there is accountability for the use of chemical weapons so that it never happens again."
It's a far cry from 1988 when people like Hiltermann were critical of the world for doing nothing about Halabja and of the UN for bowing to American pressure to not hold Iraq responsible for being the first country to use poison gas against civilians, despite the realized threat of proliferation.
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