The United Nations late on Thursday confirmed that chemical weapons had been used in the almost three year Syrian conflict, with experts investigating more than half a dozen alleged uses of proscribed weapons and – in what CNN described as “the case that was most clear” – documenting an August incident near Damascus.

“The United Nations Mission collected clear and convincing evidence that chemical weapons were used also against civilians, including children, on a relatively large scale in the Ghouta area of Damascus on 21 August 2013,” read the 82-page report, which was released on Thursday. Blood and urine samples from patients there tested positive for sarin and sarin signatures, it found. Anti-government activist groups say more than 1,300 people were killed in the attack in Ghouta — many of them women and children. Graphic video footage showed rows of bodies without apparent injury, as well as people suffering convulsions or apparently struggling to breathe.

The report comes amid deepening controversy over the context and scope of upcoming Geneva II talks designed to facilitate a resolution to the conflict, with news emerging that over 30 countries, among them Iran and Saudi Arabia, invited to attend. The two states are respectively the key backers of the Bashar al-Assad regime and of elements of the opposition seeking the regime’s overthrow. Riyadh has been accused, less so than Turkey and Qatar but more so than the West, of providing support to extremist elements at the expense of more moderate Western-backed forced. The consistent erosion of U.S.-backed fighters became particular pointed this week, with a top commander of the Free Syrian Army being forced out of the country as Islamists overran the positions of the Free Syrian army (FSA). Reuters reported today that the relative power dynamics inside Syria had forced the opposition to seek the protection of Al Qaeda-linked groups.

[Photo: ABC News / YouTube]