Non-conventional war in Syria? Security forces loyal to President Bashar Assad have been using chemical weapons against Syrian rebels, under the supervision of Iranian and Russian experts, a defecting Syrian officer charged Monday.

The officer, Captain Abd al-Salam Ahmed Abdul Razek, who served in Syrian's chemical warfare administration, told al-Arabiya that the Syrian military used nerve gas – banned by various international conventions – in order to assist forces in their raid on the restive city of Homs.

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The defecting officer added that the Syrian army's Fourth Division and Republican Guard are expected to use chemical weapons elsewhere. Assad's forces have access to toxins produced by Russia and a small quantity of them may cause numerous casualties, he said.

The nerve gas was used under the supervision of Russian and Iranian experts, who told the army when and how to utilize the chemical weapons, the officer added.

Meanwhile, Syrian opposition sources said that 25 people were killed during the day by army forces loyal to President Assad. The sources added that the massive bombardment of the city of Homs continues unabated.

On Sunday, 36 civilians were killed by security forces across Syria.