The death toll was recorded between April 23 and May 23. The past month’s aerial operations represent the largest number of one-month casualties inflicted by the US-led coalitional thus far.
Among the dead were 44 children and 36 women, SOHR claimed while also underlining that some 220 Syrian civilians were killed by the US military the month before.
The US-led air campaign against the Islamic State began back in late 2014. Since then, an estimated 1,481 civilians – including 319 children – have been killed by the US Air Force’s raids across the war-torn country.
Earlier this month, the US military said that coalition air strikes in Iraq and Syria had “unintentionally” killed 352 civilians since the campaign began.
On Friday, US Defence Secretary Jim Mattis said President Donald Trump has instructed the Pentagon to “annihilate” ISIS in Syria in a bid to prevent foreign fighters from returning home.