Barack Obama warns Syria chemical arms a 'game changer'
27 April 2013 Last updated at 09:08 BST
US President Barack Obama has vowed a "vigorous investigation" into reports that Syria has used chemical weapons, warning they will be a "game changer" for US policy if proven true.
Both the US and UK have pointed to emerging evidence that Syria has used weapons such as the nerve gas sarin.
Syrian officials have denounced the allegations as "lies".
According to the UN, at least 70,000 people have been killed in the two-year uprising against Syrian President Bashar al-Assad.
David Willis reports.