David Cameron has said there is credible evidence of "multiple attacks" using chemical weapons by Syrian President Bashar Assad's regime.
The Prime Minister said the UK believes the "scale of use is sanctioned and ordered by the Assad regime" but also indicated that al-Qaeda-linked elements in the opposition movement had also attempted to acquire chemical weapons for probable use in Syria.
He restated the Government's position that no decision had been taken to arm moderate rebels opposed to Assad, but added that he was a "brutal dictator who is using chemical weapons under our nose".
US President Barack Obama has tip-toed over the 'red-line' and armed Syrian rebels but it is a gamble of huge proportions.
Writing for ITV News, international affairs analyst David Butter looks at the timing of US support for Syria and when it may arrive.
Are the US supplied assault rifles too little, too late and what incentive is there for Assad to enter peace talks?