By Dasha Afanasieva
ISTANBUL, Sept 10 (Reuters) - A Syrian forensic expert who defected to Turkey last month said on Tuesday he had documents confirming President Bashar al-Assad's government had used chemical weapons near Aleppo in March, and called their use "cold murder".
Abdeltawwab Shahrour, head of the forensic medicine committee in Aleppo, appeared in public for the first time since his defection to Turkey was confirmed by the Istanbul-based Syrian opposition coalition a week ago.
Shahrour failed to show up at a planned news conference last Tuesday due to concerns over his safety, the coalition said.
He told reporters in Istanbul that he had evidence of the March 19 chemical attack in Khan al-Assal near Aleppo.
Washington is considering military strikes over a another alleged chemical weapons attack near Damascus last month that killed hundreds of people, although Russia this week proposed an alternative plan to win Syria a reprieve.
"We have examined thousands of bodies of victims which the head of forensic medicine received in Aleppo," Shahrour said. "I thought that was cold murder. I contacted some of the rebels and documented these crimes.
"One of the most horrific attacks was Khan al-Assal. Many victims showed nervous symptoms, like convulsions. Results show that they have been exposed to poison gas," he said, adding that he had documents showing the government was behind the attack.
The attack at Khan al-Assal in the northern province of Aleppo killed more than two dozen people. Both the government and rebels have blamed each other for what they say was an attack involving chemical weapons.
Russia, which alongside Iran is Syria's closest ally and chief arms supplier, said in July its own scientific analysis indicated the attack had involved the nerve agent sarin and had most likely been carried out by the rebels.
Shahrour said he decided to defect 10 months ago but only managed to begin his escape on Aug. 15, when he was brought to a safe house inside Syria in cooperation with the rebels. He arrived in Turkey three days later.
Rebels fighting Assad's forces brought his family to Turkey later. He denied reports he had been kidnapped. (Writing by Jonathon Burch; editing by Mike Collett-White)