In a Saturday report, the Syrian Network for Human Rights said the September fatalities included 192 children and 163 women.
“Some 57 civilians were tortured to death by regime forces in September,” the report said.
According to the NGO, airstrikes carried out by Russia – a major ally of the Bashar al-Assad regime – killed 391 civilians in Syria in September, including 114 children and 54 women.
“Regime and Russian forces have violated human rights law that guarantee the right to life,” the NGO said.
The report said that around 99 civilians, including 17 children, were killed by Daesh militants.
Opposition groups killed 38 civilians, including 19 children, while 14 people were killed by U.S.-led coalition airstrikes in September, the NGO said.
The report went on to note that two civilians, including a woman, were killed last month by PYD, the Syrian wing of the PKK terrorist group.
Syria has been locked in a vicious civil war since early 2011, when the Assad regime cracked down on pro-democracy protests -- which erupted as part of the "Arab Spring" uprisings -- with unexpected ferocity.
The Syrian Center for Policy Research, a Beirut-based NGO, has put the total death toll from the five-year conflict at more than 470,000.