At least 30 civilians were killed in air strikes on an area of eastern Syria held by the Islamic State group on Wednesday.
It was not immediately able to say whether the strikes in Deir Ezzor province were carried out by the US-led coalition, or by the Syrian army or its Russian ally.
They came just two days after a suspected coalition strike on an IS jail in the province killed 42 prisoners and 15 jihadists, according to an Observatory toll.
Today’s strikes hit an area 20 kilometres (12 miles) east of Mayadeen, the town where the prison bombing took place.
Most of Deir Ezzor province is controlled by the jihadists and it has been the target of air strikes by the US-led coalition as well as the Syrian army and Russia.
The coalition has been hitting IS in both Syria and Iraq since mid-2014 and the jihadists are under growing pressure in both countries.
Syria’s war has killed more than 320,000 people and forced millions from their homes since it began in March 2011 with anti-government protests.