At least 58 people have been killed and dozens wounded in a suspected chemical attack on a rebel-held town in north-western Syria.

The Syrian Observatory for Human Rights reported that strikes on Khan Sheikhoun by Syrian government or Russian jets had caused many people to choke.

The Syrian government has repeatedly denied using chemical weapons.

However, an investigation by the United Nations and the Organisation for the Prohibition of Chemical Weapons concluded last October that government forces had used chlorine as a weapon at least three times between 2014 and 2015.