"On Tuesday, 50 inmates including seven women were set free from Adra prison and 84 others from Hama prison," Michel Chammas, who represents many of them, told AFP by phone from Germany.
"Another 31 inmates at Homs prison were also informed that they are going to be let go but they still haven't been released. Four others held elsewhere should also be released," he said.
Those being freed had been accused of "terrorism", a term President Bashar al-Assad's government uses to describe all of its armed opponents.
Two officers and three crew were aboard a Russian military helicopter shot down on August 1 in the northwestern province of Idlib, which is almost entirely under the control of a coalition of Islamists and jihadists.
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The attack was the single deadliest for Moscow since it intervened in the conflict in September 2015 in support of Assad, taking to 18 the overall number of Russian soldiers killed in the country.
The Syrian Observatory for Human Rights, a monitoring group, said 86 people had been released in the central city of Hama.
They had been accused of "terrorism" or involvement in anti-regime protests at the outbreak of Syria's conflict in 2011, said the Britain-based monitor, which has a network of sources on the ground in Syria.
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