A Russian helicopter has been shot down by rebels in northern Syria, Russian military officials say.
Defence officials say the Mi-8 transport aircraft had five people on board. Unconfirmed reports say at least four of them are now dead.
It is not clear which group brought the helicopter down.
Pictures on social media purportedly of the aftermath of the crash show charred wreckage and bodies, with armed men milling around.
Russia is a key backer of Syrian President Bashar al-Assad and is supporting pro-government forces with air strikes on rebels.
Government forces cut off rebel-held eastern parts of Aleppo last month.
Russia and Syria announced the opening of what they called humanitarian corridors for civilians and rebels wanting to surrender, but few people are reported to have used them, fearing they would be targeted.