Over the past month, air-strikes carried out by the US and its coalition partners in Syria have killed the highest number of civilians on record since the bombing campaign began in September 2014, according to the UK-based Syrian Observatory for Human Rights. A total of 225 civilians, including 36 women and 44 children, were killed in the period between April 23 to May 23 by the Observatory's count. At least 122 ISIS fighters and eight members of militias loyal to the Syrian regime were also killed in US-led strikes over the same period.

"The past month of operations is the highest civilian toll since the coalition began bombing Syria," Observatory head Rami Abdel Rahman told AFP news agency. "There has been a very big escalation."

Earlier this month, the Pentagon said that coalition air-strikes in Iraq and Syria had "unintentionally" killed 352 civilians since the campaign began, but rights groups have criticized the estimate as too low. SOHR's own estimate is that 1,481 people, including 319 children, have been killed in US-led air operations since 2014. (The Independent)

Russian air-strikes in Syria have resulted in a far greater number of casualties since Moscow launched its own air campaign in 2015.