Secretary of State John Kerry called the "indiscriminate slaughter" of civilians in Syria using chemical weapons a "moral obscenity" in a speech two weeks ago. His words were largely dismissed by the international community, which declined to get behind U.S. airstrikes against the country.

For many nations, the outrage over the attack brought back memories of a different U.S. approach to the use of chemical weapons.

As Foreign Policy reported last month, secret CIA files prove that the U.S. helped Saddam Hussein target and then cover up Iraq's use of chemical weapons against Iran during the 1980s.

U.S. officials delivered satellite intelligence to Iraq that enabled the country to target Iran's forces with both chemical and conventional weaponry, in an effort to win the war against the Islamic Republic.

The intelligence sharing started early, Thomas Twetten, a CIA officer at the time, recalled, according to a transcript of a conference printed in a recent book.

"I was a messenger who was sent to Baghdad in the summer of 1982 to deliver satellite imagery -- maps, battle line imagery -- to the Iraqis," Twetten said, according to the book. "My instructions were 'do not ask for anything in return'; this was an American gift."

The book, Becoming Enemies: U.S.-Iran Relations and the Iran-Iraq War, 1979-1988, resulted from a major conference held on U.S. involvement in the Iran-Iraq war. It includes contributions from James Blight, Janet Lang, Hussein Banai, Malcolm Byrne, John Tirman and Bruce Riedel.

By 1984, the United States knew of Iraq's first chemical weapons attacks. But in 1987, according to Foreign Policy, the intelligence was still flowing. The Iraqis used a U.S. intelligence report in a series of gas attacks near the city of Basra utilizing sarin, the same agent the U.S. has tagged as the gas used outside of Damascus in Syria.

Iraq's chemical weapons ultimately killed a reported 20,000 Iranian soldiers.

"Did we do enough to resist Iraqi use of chemical weapons? I think the answer is no ... concern about Iraq losing the war was powerful. This concern seemed to overwhelm everything else," Ambassador Richard Murphy, who was an assistant secretary of state involved in crafting the administration's response to the Iraq-Iran war at the time, said the transcript of a conference recorded in Becoming Enemies.

"Our feeling that an Iranian victory in the war would become some sort of Middle Eastern Armageddon even skewed our view of what was humane and what was inhumane," Murphy said.

Even after the horrific Iraqi gassing of Kurds in Halabja in 1988 in which 3,200 to 5,000 people, mostly civilians, were killed, the State Department blamed the Iranians.

"The result of this stunning act of sophistry was that the international community failed to muster the will to condemn Iraq strongly for an act as heinous as the terrorist strike on the World Trade Center," Joost Hiltermann, who investigated the attack for Human Rights Watch, wrote in 2003.

Israel, too, may have produced chemical weapons at one point, according to a secret CIA intelligence estimate from 1983 that Foreign Policy also first reported. Israel signed the Chemical Weapons Convention in 1993, but it has never ratified it, preferring instead to wait for other countries in the Middle East to join it. Those two countries: Egypt and Syria.

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