Russia has denied its warplanes carried out air strikes on a village in eastern Syria on Sunday, which activists say killed dozens of civilians.
The Syrian Observatory for Human Rights said 53 people died in al-Shafah, while website DeirEzzor24 put the toll at 25.
Both said Russian aircraft, which are supporting Syrian pro-government forces battling so-called Islamic State (IS) in the area, were behind the attack.
But on Monday Russia’s defence ministry insisted it did not bomb al-Shafah.
“The Russian Aerospace Forces’ strikes in Syria target areas outside population centres, and only facilities of the international terrorist groups,” a statement said, according to Russian news agencies.
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“Information about such facilities is checked before the strikes are carried out and verified in real time via several channels, both from the ground and by unmanned aerial recording devices,” it added.
“The reports by the Syrian Observatory for Human Rights, which is based in Great Britain, about the alleged strikes by the Russian Aerospace Forces’ planes on the village of Shafah are yet another fake.”
An earlier statement had announced that six Russian Tu-22M3 long-range bombers struck IS command posts and militant positions in Deir al-Zour province on Sunday.
DeirEzzor24, an activist-run news website, reported that Sunday’s air strikes targeted a residential compound where several displaced families were staying.
Most of the 25 people killed were women and children, it said, adding that the death toll might rise because many victims were still trapped under collapsed buildings.
The Syrian Observatory, which relies on a network of sources inside Syria, also said residential buildings were hit and that 21 children were among the fatalities.
Al-Shafah is located on the eastern bank of the River Euphrates, about 110km (68 miles) south of the city of Deir al-Zour and 14km from the border with Iraq.
It is just to the north of the town of Albu Kamal, which Syrian soldiers and pro-government militiamen captured earlier this month with Russian air support.
The Syrian Air Force and warplanes from a US-led multinational coalition against IS are also carrying out air strikes in the province.