Russia's Defense Ministry says its warplanes did not launch an air strike that hit a marketplace in eastern Syria on June 6 and reportedly killed at least 17 civilians.
At least eight children were reported to be among those killed by the attack, which came on the first day of the holy Muslim month of Ramadan.
The London-based Syrian Observatory for Human Rights said Russian or Syrian government planes were suspected of launching the air strikes in the town of Al-Shaara in Syria's eastern province of Deir Ez-Zor.
But Defense Ministry spokesman General Major Igor Konashenkov told Interfax that Russian planes did not carry out any combat missions in the area on June 6.
Meanwhile, Russian Foreign Minister Sergei Lavrov vowed to "actively support" Syrian troops from the air around Syria's northwestern city of Aleppo.
His remarks came after a weekend of fierce fighting that left dozens dead in the divided city.
Based on reporting by Reuters, AP, AFP, TASS, and Interfax