Britain has joined the United States in warning Syria that the use or threat of chemical weapons would force it to revisit its approach to the country.
The warning came after a telephone call between British Prime Minister David Cameron and United States President Barack Obama, the BBC reports.
Mr Cameron also spoke to French President Francois Hollande.
The three discussed building support for the opposition.
Earlier, Chinese state media accused Mr Obama of using the chemical arms issue as an excuse for military intervention.