The Syrian army tested missile systems for poison gas shells at the end of August, eyewitnesses told Der Spiegel.
On Monday the German news magazine quote witnesses as saying that the tests were conducted near a chemical weapons research center at Safira, east of Aleppo.
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According to statements from various witnesses, a total of five or six empty shells devised for delivering chemical agents were fired by tanks and aircraft at a site called Diraiham in the desert near the village of Khanasir.
The witnesses said Iranian officers believed to be members of the Revolutionary Guards were flown in by helicopter for the testing.
Der Spiegel said the Safira research center is regarded as Syria's largest testing site for chemical weapons. It is officially referred to as a "scientific research center."
It has been reported that scientists from Iran and North Korea to work in the expansive, fenced-off complex.
According to Western intelligence agencies, they produce chemical agents such as sarin, tabun and mustard gas and test them on animals, the German magazine said.
Der Spiegel further reported that in recent months the guards at the site have been replaced and reinforced by more than 100 elite troops from the 4th Tank Division in case rebels try to attack it.
But according to a former army officer who deserted and joined the Free Syrian Army, the rebels do not plan to take the site.
"We hope American troops will secure the plant," he was quoted by Der Spiegel as saying. "We don't want the regime to be able to use the weapons, but neither do we want them to fall into the hands of radicals after the downfall (of the regime)."
Syria is believed to have one of the world's largest arsenals of chemical weapons.
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