Observers claim the number is higher than those killed by Russian strikes, Isil and President Bashar al-Assad’s forces in the same period.   

Rami Abdel Rahman, SOHR’s director, said that the new deaths brought the overall civilian toll from the coalition’s campaign in Syria to 1,953, including 456 children and 333 women.  

Human rights and monitoring groups have warned for months of the rising human cost of the coalition’s air war, particularly as the battle for Isil’s so-called capital of Raqqa intensifies.

The US, UK and other coalition members have provided air support for allied Syrian Democratic Forces (SDF) on the ground.  

The coalition insists it takes every measure to avoid hitting civilians, but residents say they are increasingly becoming collateral damage.  

“We note in particular that the intensification of airstrikes, which have paved the ground for an SDF advance in Raqqa, has resulted not only in staggering loss of civilian life, but has also led to 160,000 civilians fleeing their homes and becoming internally displaced,” Paulo Sérgio Pinheiro, chairman of the UN Independent International Commission of Inquiry on Syria, said earlier this month.   

In March, more than 200 mostly women and children were reported to have been killed while they seeking refuge in a school building in the village of Mansoura.

Alarmingly high civilian tolls are also being reported in the Iraqi city of Mosul, where the battle to dislodge the jihadists is in the final throes. 

In one, now notorious incident, more than 150 civilians were killed on Match 17 when a 500lb bomb was dropped on a house to kill two Isil snipers on its roof. 

The rise in reported fatalities raises questions about whether once-strict rules of engagement meant to minimise civilian casualties were being relaxed under the Donald Trump administration, which has vowed to fight the Islamic State more aggressively.