Dozens of civilians have been killed since Sunday in suspected Russian air strikes along the River Euphrates in eastern Syria, activists say.
Jets are reported to have hit camps for displaced people on the western bank of the river and passenger ferries outside the city of Deir al-Zour.
It was not possible to verify the reports, and Russia has not commented.
But it is providing air cover to Syrian government forces battling so-called Islamic State in the Euphrates valley.
Last week, troops and militiamen broke a long-running siege by the jihadist group of a government-held enclave in Deir al-Zour and a nearby military airport.
They are now seeking to advance southwards along the western side of the Euphrates to the town of Albu Kamal, which is on the border with Iraq.
A US-backed alliance of Kurdish and Arab fighters, the Syrian Democratic Forces, has launched a separate offensive in the same direction on the eastern bank.
The Syrian Observatory for Human Rights, a UK-based group that monitors Syria's civil war through a network of sources, said on Tuesday that at least 69 people had been killed in suspected Russian air strikes over the past 72 hours.
On Sunday it reported that 34 civilians, including nine children, had died in a raid that destroyed more than 40 ferries waiting to transport passengers across the Euphrates between the IS-held town of al-Baloul and al-Sakhba, 25km (15 miles) south-east of Deir al-Zour.
The activist-run website DeirEzzor24 put Monday's death toll at 17 and also blamed Russian warplanes.
Local clinics were struggling to cope with the injured because of a shortage of staff and medicines, it said, adding that civilians were forced to use the ferries to flee the fighting in the area because all the bridges had been destroyed by IS.
On Monday, the Syrian Observatory said another 19 civilians had been killed in suspected Russian air strikes on tents where displaced people were sheltering in the village of al-Khurayta, 16km (10 miles) north-west of Deir al-Zour, and on boats at a nearby river crossing to Hawayij Dhiyab Shamiya in Iraq.
DeirEzzor24 later listed the names of 27 people it said were killed in these raids.
The Syrian Observatory said another 16 civilians, including five children, had been killed on Tuesday in a Russian air strike on a cluster of tents in Zaghir Shamiya, north-west of Deir al-Zour.
It also reported that US-led coalition aircraft had bombed al-Shahabat, killing 12 members of a single family, during fierce fighting around the village between IS and the US-backed Syrian Democratic Forces.
DeirEzzor24 put the death toll in Zaghir Shamiya at eight and said a number of civilians had been killed in al-Shahabat, but it did not say who was responsible.