The Syrian Army has reportedly test fired five or six shells developed to deliver chemical agents in the desert near one of its major cities, according to the German news magazine Der Spiegel.

The tests, which took place at the end of August, were fired by tanks and aircraft near a chemical weapons research center in Safira east of Aleppo, the publication reports, citing witness accounts.

With Syria beset by a bloody civil war, Israeli officials have been concerned that President Bashar al-Assad may use chemical weapons to put down the 18-month uprising — or that chemical weapons may fall into the wrong hands, reports The Jerusalem Post.

This chemical weapons test reportedly took place at a site called Diraiham in the desert near the village of Khanasir and included observers from Iran’s Revolutionary Guard.

Iran has been a long-standing ally of Syria dating back to Syria’s support of the country in its war with neighboring Iraq in the 1980s, according to Der Spiegel, which notes that the Safira facility is believed to produce sarin, tabun, and mustard gas.

Both sarin and tabun are classified as Weapons of Mass destruction by the United Nations.

Assad has controlled Syria since shortly after the death of his father in 2000. The uprising began in March 2011 with the Arab Spring.