The victims were found exactly where they had been when the gas hit. Their silent killer had given little warning.

One father had a protective arm around his young wife and baby. An infant in nappies was still holding his older brother’s hand.

None bore any sign of injury. They would have looked peaceful in sleep if not for their blushed cheeks and frothing mouths.

Several families had been seeking shelter in a house in the Syrian town of Douma, in what remains of rebel-held Eastern Ghouta, when what is thought to be a chemical bomb struck its roof at 8.45pm on Saturday.

Rescuers who reached the house knew immediately this attack was different.