A Syrian man checks the site of Syrian government bombardments in Hamouria, in the besieged Eastern Ghouta region on the outskirts of the capital Damascus, on Thursday. Pic/AFP

Syrian President Bashar al-Assad has committed "war crimes" with Russian support against his own people, the US said on Friday, as it put the Assad regime as well as Russia "on notice" following massive civilian casualties in rebel strongholds of the strife-torn country.