A Russian soldier has died while serving in Syria although the cause of his death was unclear, two people close to his family told AFP on Tuesday, but there was no official confirmation.

Vadim Kostenko, 19, from the southern Krasnodar region, "went to Syria as a contract soldier," a person close to the family said by phone from Krasnodar.

"He is dead," said the person, adding that the cause of the death was unclear and that he may not have died in combat.

The family friend said he had learnt of Kostenko's passing on Saturday.

The soldier is expected to be buried "in the middle of the week," he said, declining to be identified because of the sensitivity of the matter.

Grigory Donskikh, who served with Kostenko in Russia and knows him well, confirmed his death but said he did not know how he died.

"He has not arrived yet," Donskikh said, referring to Kostenko's body.

On September 30, Russia launched a bombing campaign in Syria, saying it needed to target Islamic State militants before they cross into Russia.

Russian warplanes have carried out sorties from the Hmeimim airbase in government-held territory in Latakia and Russian servicemen are based there to help service the aircraft, among other talks.

Russia insists that its ground troops are not taking part in combat operations in Syria and there have been no official reports of any servicemen dying while on duty in the war-torn country.
- Official silence -
The defence ministry in Moscow declined to comment when asked about Kostenko by AFP on Tuesday.  

A spokeswoman for the foreign ministry, Maria Zakharova, said: "We don't have any information."

President Vladimir Putin's spokesman Dmitry Peskov also told reporters that he knew "nothing about" the possible deaths of any Russian soldiers in Syria and referred all questions to the defence ministry.

A member of the Kremlin's rights council, who advocates for the rights of soldiers and works with the defence ministry, told AFP on Tuesday that he was not aware of Kostenko's death.

But the rights activist, Sergei Krivenko, said that his defence ministry sources told him "about 10 days ago" that a Russian soldier had died "at the base" in Syria.

"It was either an illness or trauma," said Krivenko, the head of the Citizen and the Army rights group.

On Friday, The Wall Street Journal reported that one Russian soldier had "died in Syria due to careless handling of weaponry."

Russian officials have previously denied accusations from Kiev and the West that it sent regular troops to eastern Ukraine to prop up pro-Kremlin insurgents during an 18-month conflict.

The state enforced a virtual blackout on reports of Russian soldier deaths in Ukraine despite multiple reports to the contrary including funerals of soldiers.

Source: AFP