The three crew and two officers from Russia's reconciliation centre were returning to base. The condition of those on board was yet to be established, the ministry said.

"On August 1, an Mi-8 transport helicopter has been shot down by ground fire in Idlib province after a delivery of humanitarian aid to the city of Aleppo. Three crew members and two officers from the Russian Reconciliation Centre in Syria were on board," the Defence Ministry said in a statement.

The helicopter was returning to the Russian air base at Khmeimim, the statement added.

The ministry has not yet revealed the identities of those on board. It was the third Russian helicopter lost in action in Syria this year.

In July, an Mi-25 attack chopper was shot down near Palmyra, killing two Russian pilots. The aircraft had been engaging the advancing Islamic State militants at the Syrian Army's request when it was taken down, according to the Russian Defence Ministry.

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

Last October, another Mi-8 helicopter was badly damaged and then destroyed by IS fighters after an emergency landing in the middle of search and rescue operation to extract a surviving co-pilot of a Su-24M bomber jet shot which was downed by a Turkish Air Force F-16.

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