A monitor group says air strikes by Russian jets have killed at least 53 civilians, including 21 children, in a village held by the Islamic State (IS) extremist group in eastern Syria.
The Britain-based Syrian Observatory for Human Rights said the attack occurred early on November 26 in the Deir al-Zor Province. It earlier had said the death count was 34.
Observatory chief Rami Abdel Rahman said the strikes hit "residential buildings" in the village of Al-Shafah on the eastern bank of the Euphrates River, adding that at least 18 people were wounded in the attack.
The report could not immediately be independently verified.
On November 27, Russia's Defense Ministry denied that Russian war planes had targeted Al-Shafah.
The observatory relies on a network of sources inside Syria and says it determines what country’s planes carry out attacks based on type, location, flight patterns, and weapons used.
Russia supports the government of President Bashar al-Assad and provides air support for regime forces. Iran also backs Assad in the six-year civil war, while the United States and Turkey support differing antigovernment rebel groups.
IS also entered the war and is opposed by all other sides. It has been driven out of most of its strongholds in the country, with Deir al-Zor Province one of the last remaining areas where its fighters are holding out.
The report of the strike comes as so-far mainly fruitless efforts to end the bloody conflict in Syria have intensified.
The United Nations is holding talks in Geneva with a goal of finding a political solution to the war. The eighth round of those negotiations are due to start on November 28.
Meanwhile, talks sponsored by Russia, Iran, and Turkey are also being held in the Kazakh capital, Astana, to deal with battlefield issues, such as cease-fires and the creation of "de-escalation zones." The zones have led to reduced violence in many areas, although deadly air strikes have continued.
Russia, Iran, and Turkey have also proposed holding a "national congress" of government and opposing forces in the Russian city of Sochi, although no date has been set.
More than 330,000 people have been killed in Syria and millions have been driven from their homes since the conflict began in March 2011 with a crackdown on antigovernment protests.