The Russian ambassador to Ankara was shot in the back and killed while giving a speech at an art gallery on Monday. Turkish security sources said the gunman, who shouted "Don't forget Aleppo", was an off-duty police officer. The Russian foreign ministry confirmed the death of envoy Andrei Karlov, which marked one of the most serious spillovers of the Syria conflict. Turkey has struggled with a string of attacks by Islamist and Kurdish militants but the killing of a Russian envoy could have resonance throughout the region. Russia is a close ally of Syrian President Bashar al-Assad and its air strikes were instrumental in helping Syrian forces end rebel resistance last week in the northern city of Aleppo. President Tayyip Erdogan, however, has been a vociferous opponent of Assad. "We regard this…