The group said at least 498 civilians were among those killed in Syria since the government and opposition joined peace talks that were due to wrap up later Friday, having produced no signs of progress.
The civilian deaths included 431 killed in fighting between rebels and the government, as well as 40 who died from lack of food and medicines in areas under government siege, the Observatory said.
Another 27 civilians were killed in clashes between the jihadist Islamic State of Iraq and al-Sham and rival rebels that began at the beginning of January.
The group said 646 mainstream or Islamist rebels had been killed in fighting with regime forces or the ISIS.
Another 208 rebels from ISIS and the al-Qaeda -affiliated Al-Nusra Front died in clashes with regime forces, rival rebels or Kurdish militia, the Observatory said, adding that three Kurdish militiamen were also killed.
On the government side, 515 combatants were killed – soldiers, allied militia or Iraqi Shiite volunteers – the NGO said.
The fighting in Syria has shown no let-up since the regime and opposition began long-planned peace talks in Switzerland, first in the town of Montreux and later in Geneva.