Russia has confirmed the death of one of its soldiers in Syria for the first time since the Kremlin launched a campaign of airstrikes.

The parents of Vadim Kostenko told Reuters they had been informed their son had hanged himself on his base at the end of a shift - but they said they did not believe the Russian Defence Ministry's explanation.

The death was uncovered by Conflict Intelligence Team, a group tracking Moscow's military involvement in Ukraine and Syria.

They said the soldier had been killed in service and was due to be buried in his home village of Grechanaya Balka "soon".

Russian defence chiefs said an investigation was ongoing but analysis of Kostenko's phone messages indicated he took his own life because of a break-up with his girlfriend.

Kostenko's mother Svetlana said she had spoken to her son on Saturday and would "never" believe he killed himself.

She said: "We spoke every day by phone for half an hour. He was cheerful, happy and he laughed."

His father, Alexander, added: "We were told he had hanged himself because of a girl. He would never have done it. I know my son really well." 

The death may test how Moscow explains military deaths to the public.

The Syria campaign has had huge coverage on state TV and opinion polls have put support for the campaign as high as 70% - but that could change if the conflict drags out or there are serious fatalities.

Kostenko - one of the Russian air force's support staff - had signed a contract on 20 June and was sent to Syria on 14 September, two weeks before the bombing campaign in support of President Bashar al Assad began.

His younger sister Katya and aunt Anna Musienko said they also did not believe he would have killed himself.

They said he was planning to marry his girlfriend, who he had introduced to his family during the summer.

Kostenko's girlfriend still appears to feature in his profile picture on the Russian social network VKontakte.