Five Russians on board a military helicopter were killed when it was shot down by rebels in northern Syria, Russia has said.
The Mi-8 transporter came down in Idlib province. It was carrying three crew and two officers, Russia’s defence ministry said.
The helicopter was returning from delivering humanitarian aid to the besieged city of Aleppo, it said.
It is not clear which group brought the helicopter down.
An alliance of rebel groups, including hardline jihadist factions, is the dominant power in Idlib.
Pictures on social media purportedly of the latest Russian helicopter downing showed burning wreckage and bodies, with armed men milling around.
Footage showed at least one body being dragged away. Another is seen apparently being trampled on.
This is the single worst loss of life for Russia since it launched its air offensive in Syria in support of President Assad towards the end of last year.
Moscow says the helicopter was not involved in a military mission, but was delivering humanitarian aid.
That claim may be open to question as Russia has mostly used its air power to back military offensives by pro-government forces in Aleppo and elsewhere. But it will further inflame feelings in Russia against rebels in Syria. Moscow has repeatedly said it sees little distinction between the rebels in terms of brutality and extremism.
Graphic images posted online of the aftermath of the incident will add fuel to the fire.
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.
Opposition activists have dismissed as a lie Russian claims that 160 civilians had left rebel-held districts.
The United Nations has warned that basic supplies for the around a quarter of a million people who live in besieged areas will last only three weeks.
On Sunday, rebel groups south of Aleppo launched a push to try to break the siege, in what observers said was one of the biggest counter-offensives in months.
In a further reminder of the plight of civilians in Aleppo, it has emerged that a child star of a popular TV sitcom filmed in the city has been killed in the violence.
The comedy, Um Abdou the Aleppan, has been likened to I Love Lucy, the American series involving a housewife frequently at odds with her husband.
Fourteen-year-old Qusai Abtini played the husband in Um Abdou the Aleppan, which is produced in rebel-held districts, has a cast comprised entirely of children and takes a wry look at everyday life in the city.
Qusai Abtini’s father decided in early July to evacuate his children, but the car his son was riding in was reportedly hit by a missile.
Credit: BBC & AlJazeera