A Russian military helicopter has been shot down in Syria's rebel-held Idlib province killing all five people on board, in the biggest officially acknowledged loss of life for Russian forces since they started operations in Syria.
Images on social media purportedly taken at the scene of the crash on Monday showed a dead body stripped of clothing being dragged through the dirt near the wreckage.
Russian identity documents purportedly taken from the helicopter could also be seen.
Russia's defence ministry said the Mi-8 military transport helicopter had been shot down after delivering humanitarian aid to the city of Aleppo as it made its way back to Russia's main air base in the western province of Latakia.
"As far as we know from the information that has reached the defence ministry, those on board died, they died heroically," Kremlin spokesman Dmitry Peskov said in a conference call with reporters.
The helicopter came down near the town of Saraqeb, in Idlib province, roughly mid-way between Aleppo and the Russian air force base at Khmeimim, near the Mediterranean coast.
No group has claimed responsibility for shooting down the helicopter.
Islamic State fighters are not active in the area, but there are other Islamist rebel groups there, as well as moderates backed by the United States and its allies.
That raises the prospect -- which could cause a major diplomatic incident -- of the helicopter having been brought down by a US-supplied weapon.
The United States has equipped some rebel groups with TOW anti-tank missiles, which can also be used against helicopters.
Russia's military has since September last year been supporting President Bashar al-Assad in Syria's five-year-old civil war.
In Aleppo, around 40 km north-east of the crash site, rebel groups are under siege from government forces backed by Russian air support.
Rebel groups are staging an offensive to try to break the siege.
Moscow said last week it was opening humanitarian corridors for civilians to leave the rebel-held areas, and for fighters to give up their arms.
However, rebel activists and aid groups have expressed scepticism, saying Russian aircraft are bombing the city and causing civilian casualties.
US officials have suggested the plan may be an attempt to depopulate the city so that the Syrian army can seize it.
Russian denies targeting civilians.
Despite persistent Western accusations that Moscow is abetting Assad in a brutal crackdown on his own people, Russian President Vladimir Putin has presented the Syrian operation as a success in the fight against Islamist terrorism.
