At least 57 people were killed when US-led coalition airstrikes struck a jail run by the Islamic State group in eastern Syria, the Syrian Observatory for Human Rights claimed on Tuesday.

The militant-held prison is situated in al-Mayadeen, which lies in the Euphrates Valley some 45 kilometres (28 miles) southeast of the provincial capital of Deir az-Zor.

"The strikes hit an IS jail in Mayadeen at dawn on Monday, killing 42 prisoners and 15 jihadists," observatory chief Rami Abdel Rahman told AFP.

The strikes come just a day after at least 12 civilians were killed on Monday when a suspected Russian airstrike struck the town of Qouriya in the eastern Syrian town of Deir az-Zor.

Local sources told The New Arab that an aircraft, believed to be Russian, struck at civilian houses with highly explosive missiles in the town of Qouriya, killing 12 civilians, including women and children.

A total of more than 320,000 people have been killed since Syria's conflict erupted in 2011 with anti-government protests, according to the UK-based Observatory.

Earlier this month, the Syrian Observatory for Human Rights said US-led coalition airstrikes on two Syrian provinces targeting extremists have killed 472 civilians over the past month, more than double a previous 30-day toll.

Rahman said 260 civilians, including 82 children, were killed in the largely Islamic State group-held province of Deir az-Zor.



Another 250 civilians, including 53 children, were killed in Raqqa province, where US-backed forces are trying to oust IS from their self-declared "capital".



Rahman told AFP that the new deaths brought the overall civilian toll from the coalition's campaign to 1,953, including 456 children and 333 women.

The coalition insists it takes every measure to avoid hitting civilians, including by aborting missile strikes at the last moment if a civilian unexpectedly wanders into the target zone.



In an emailed statement, the international alliance said its forces "work diligently and deliberately to be precise" in their airstrikes.



"Our goal is always for zero civilian casualties," the statement said.