A Russian military helicopter has been shot down by rebels in Idlib, northern Syria, killing five people on board, Russia has said.
The Mi-8 chopper was carrying three crew and two officers, Russia’s defense ministry said in a statement.
The aircraft was returning from delivering humanitarian aid to the besieged city of Aleppo, the statement added.
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.
Russia has previously, though seldom, lost aircraft since it launched operations in support of the Syrian government at the end of September 2015.
In July 2016, two Russian pilots were killed when their helicopter was shot down east of Palmyra by ISIS.
In November 2015, the pilot of a Russian Su-24 fighter plane was killed when the aircraft was shot down by Turkey on its border with Syria.
A Russian marine sent on a mission to rescue the pilot was also killed when his helicopter was shot down.
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.
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.