Kerry: We know that Syrian regime has largest chemical weapon programme in the Middle East

US secretary of state John Kerry has said the government knows that the regime of Syrian president Bashar al-Assad "has the largest chemical weapon programme in Middle East" and has used them multiple times this year.

The most recent attack on 21 August left at least 1,429 dead including at least 426 children, he said.

The weapons were launched only from regime-controlled areas, and only at areas controlled by the opposition or contested areas.

Kerry said that the move to unclassify evidence was "unprecedented", although some documents had to remain secret to protect the sources.