A Russian helicopter was shot down in Syria's Idlib province on Monday, killing all five people on board, officials said.

It is the deadliest single incident for the Russian military since it became involved in the country's civil war.

Here is what we know so far:

The transport Mi-8 helicopter was shot down was shot down as it returned to a Russian air base on the Syrian coast, the Kremlin said.

Russian officials said that the vehicle had been out delivering humanitarian supplies to the battered city of Aleppo when it was struck by rocket fire from the ground.

Video footage showed people celebrating alongside the wreckage as it burned.

All five people onboard the helicopter were killed, the Kremlin said.

Two of the dead were armed forces officers while the other three were the helicopter's crew.

They "died heroically because they tried to move the aircraft away so as to minimise losses on the ground" said a Kremlin spokesman.

There was no immediate claim of responsibility for the attack.

Idlib province has a strong presence of fighters both for the al Qaida branch in Syria known as the Nusra Front and other anti-government rebels.

Rebels groups in the region have banded together to form a of a coalition called Jaish al-Fateh, or Army of Conquest, which controls much of Idlib.

Kremlin spokesman Dmitry Peskov said that Moscow would continue fighting international terrorism "on all fronts" despite threats from IS.

Russia has been supporting president Bashar al-Assad's forces as they fight rebel groups ranging from the so-called Islamic State to more moderate forces in a battle to control Syria.

Pro-government forces on the ground near the crash site are being supported by heavy air strikes in the area as they fight off an offensive by rebels.