Imagine the government of your country flying planes over your head which dump chemical bombs that kill you. That is exactly what the government in Syria is being accused of doing.
Children are among at least 100 who have died in Idlib province - but there are fears the number killed could rise to around a thousand.
Surgeon David Nott, who has worked in conflict zones including Syria, believes the highly toxic chemical sarin was used. He explained that sarin "is a chemical that stays on the skin and stays on the clothes of other people around, so the people that try to help the causalities will be affected by it as well".
Britain's foreign secretary Boris Johnson has described it as 'horrific' - and called for an investigation. "Bombing your own civilians with chemical weapons is unquestionably a war crime, and they must be held to account".