All five people on board a Russian military helicopter that was shot down over Syria on Monday are believed to have died, the Kremlin said.

The Russian Defense Ministry said the helicopter was shot down over the Syrian province of Idlib.

"A Russian Mi-8 military transport helicopter was shot down from the ground in Idlib province after delivering humanitarian aid to Aleppo," the ministry said in a statement.

"There were three crew members and two officers from the Russian reconciliation center in Syria on board," it said.

Kremlin spokesman Dmitry Peskov expressed condolences over the deaths of the five soldiers.

"As far as we know from the information we've had from the Defense Ministry, those in the helicopter died. They died heroically, because they were trying to move the aircraft away to minimize victims on the ground," he said.

Photos shared widely on social networks by Syrian opposition activists on Monday purported to depict the smoking aircraft in the desert and personal belongings of those inside, including Russian driver's licenses, passports and insurance cards, as well as Orthodox Christian icons.

The authenticity of the pictures could not be independently confirmed.

It was the third Russian helicopter lost in action in Syria this year. In July, an Mi-25 attack helicopter was shot down near Palmyra, killing two Russian pilots. The aircraft had been engaging advancing Islamic State militants at the Syrian Army's request when it was taken down, the Russian Defense Ministry said.

In April, an Mi-28N attack helicopter crashed while flying near the city of Homs, with the Defense Ministry stressing it was not shot down. The crash killed both pilots, with technical failure cited by Moscow as the likely cause of the accident.

Monday's helicopter downing was the deadliest for the Russians since Moscow began carrying out airstrikes in Syria last September.