Five people on board a Russian military helicopter have been killed after it was shot down over Syria, in the single deadliest incident for Moscow since it intervened in the war. 

The Russian Defence Ministry said the military 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 centre in Syria on board.”

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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 defence ministry, those in the helicopter died, they died heroically, because they were trying to move the aircraft away to minimise victims on the ground,” he told journalists.

It was not immediately clear who was responsible.

Mr Peskov also said Moscow would continue fighting international terrorism “on all fronts” despite threats from the Islamic State (IS) group.

On Sunday, IS posted a nine-minute video message on YouTube, calling on its members to carry out jihad or holy war in Russia.

The downing of the helicopter has brought the toll for Russian soldiers killed in the Syrian conflict to 18.

The Syrian Observatory for Human Rights, a Britain-based monitor, said the helicopter had come down along the administrative border between Idlib province in the north-west and neighbouring Aleppo.

Idlib is held almost entirely by a powerful coalition of Islamist and jihadist forces including the former Al Nusra Front, now known as the Fateh al-Sham Front after renouncing its status as Al Qaeda’s Syrian affiliate.