The Syrian Observatory for Human Rights as well as pro-Syrian government news outlets said the US-led coalition carried out the strike near the town of Al Bukamal, east of the Euphrates river, late on Thursday night.
Sana, Syria’s state news agency, put the number of dead at 30 in bombings which hit the villages of al Sousa and al Baghouz Fawkani on the river’s banks. In al Sousa, it is believed the strike hit families using an old ice factory as shelter.
Isis militants are also believed to be among the death toll.
US Central Command said it may have carried out bombings “in the vicinity” of the area.
US forces, the Iraqi air force and Western partners are still launching air support in eastern Syria to assist the Arab-Kurdish coalition Syrian Democratic Forces (SDF), in crushing the remnants of Isis.
The international coalition has been repeatedly criticised by human rights watchdogs for not taking adequate care to protect civilians in the colossal airstrikes which have helped destroy the extremist group.
Officials admitted last year that strikes against Isis in both Syria and Iraq since 2014 have killed at least 800 civilians, but credible monitoring teams put the toll at at least 6,000 people.
Although the so-called caliphate has largely collapsed, there are still believed to be around 8,000 to 10,000 Isis fighters active in the desert on the Syria-Iraq border.
Recent deadly attacks on their former Syrian stronghold of Raqqa have raised fears the militants are regrouping as an insurgency movement.