Then-Iraqi dictator Saddam Hussein (at right) behind an artillery piece during the Iraq-Iran war. (An undated photo from the 1980s.) Reuters/Landov hide caption

itoggle caption Reuters/Landov

A young man is treated at a hospital Wednesday in the Duma neighborhood of Damascus, Syria. According to activists, he was one of many casualties in what they say was a chemical weapons attack by government forces. The Syrian government has denied using such weapons. Bassam Khabieh/Reuters/Landov hide caption

itoggle caption Bassam Khabieh/Reuters/Landov

A Syrian man protesting an alleged chemical weapons attack in his homeland holds up a placard Wednesday in front of the United Nations offices in Beirut. Hussein Malla/AP hide caption

itoggle caption Hussein Malla/AP

Gas mask in one hand and rifle in the other, a Free Syrian Army fighter sits inside a house in the city of Homs early Thursday. Yazan Homsy /Reuters /Landov hide caption

itoggle caption Yazan Homsy /Reuters /Landov

An image taken from video obtained from the Ugarit News, which has been authenticated based on its contents and other AP reporting, shows an airstrike hitting the area around Damascus, Syria, early Sunday. AP hide caption

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Doctors at a hospital in Aleppo, Syria, treat a boy injured in what the government said was a chemical weapons attack on March 19. Syria's government and rebels accused each other of firing a rocket loaded with chemical agents outside of Aleppo. George Ourfalian/Reuters/Landov hide caption

itoggle caption George Ourfalian/Reuters/Landov

The White House said this week that it believes Syria has been using chemical weapons, but President Obama has not said how the U.S. might respond. Here, rebel fighters in Syria prepare to launch of a rocket in the northern Syrian city of Aleppo, on April 21. The rebels have also accused the Syrian government of employing chemical weapons. Miguel Medina /AFP/Getty Images hide caption

itoggle caption Miguel Medina /AFP/Getty Images

A top Israeli military official on Tuesday accused Syrian President Bashar Assad's regime of using chemical weapons in recent fighting in Syria. Syria has denied using such weapons. Assad is shown here at the Opera House in Damascus in January. Anonymous/SANA/AP hide caption

itoggle caption Anonymous/SANA/AP