BEIRUT (Reuters) - The head of the Syrian opposition s High Negotiations Committee (HNC) resigned on Monday, nearly two years after he was picked to chair the Saudi-backed umbrella group that brings together the armed and political opposition to President Bashar al-Assad. Riyad Hijab, a former Syrian prime minister under Assad, did not explain his reasons for stepping down in a statement posted on social media. The HNC has been the main representative of the Syrian opposition since its formation at a meeting in Saudi Arabia in December, 2015, and has taken part in U.N.-led diplomacy aimed at ending the conflict that erupted in 2011. The war has been going Assad s way since Russia sent its air force to support him militarily in 2015. The Damascus government has been steadily regaining control of territory, thanks also to the support of Iran-backed forces such as Lebanon s Hezbollah. Saudi Arabia is due to host an  expanded  conference for the Syrian opposition this month, aiming to unify its position ahead of more U.N.-backed peace talks, the Saudi state news agency SPA reported last week. Previous rounds of Geneva peace talks have failed to make headway towards a resolution of the war.      
Head of Syrian opposition's HNC resigns: statement