"The world is entitled to see evidence of chemical weapons"
UN inspectors have left Syria, carrying samples from sites of alleged chemical weapons use: http://bbc.in/1dBo4ma
Russia's President, Vladimir Putin, has challenged the US to present evidence that the regime launched an attack with the weapons.
The former inspector Hans Blix, who led a team searching for chemical weapons in Iraq between 2000 and 2003, agrees that the information must be presented.
He told BBC World Service's Newshour about the work which his successors would have carried out in Syria this week.