Russia’s Defense Ministry has raised the death toll from a military transport plane crash near the Hmeimim air base in Syria to 39.
The ministry said that according to preliminary information, 33 passengers and six crew members died when An-26 transport plane crashed while landing at the base near the coastal city of Latakia on March 6.
All of them were Russian military personnel, it added. The Russian military had previously put the death toll at 32.
Ministry officials said the crash was "most likely caused by a technical fault," adding that there were no indications the plane came under fire.
"There was no attack on the aircraft reported at the site," Russian news agencies quoted officials as saying.
Russia's Investigative Committee announced it had opened a criminal case into the crash, saying investigators would look into suggestions that flight-safety rules had been flouted.
Russia has given Syrian President Bashar al-Assad's government crucial support throughout the seven-year civil war in Syria, which began with a government crackdown on peaceful protests.
Moscow helped turn the tide of the conflict in Assad's favor by launching a campaign of air strikes in 2015 and stepping up its military presence on the ground.
More than 40 Russian military personnel died in Syria since Moscow launched its air campaign, in many cases using Hmeimim as a base, Russian officials say.
Russia is also said to have lost nine military aircraft in Syria since it entered that country's civil war.
Last month, a Russian Su-25 attack aircraft was shot down over the northwestern province of Idlib, believed to have been hit by a shoulder-launched missile.
The Defense Ministry said the pilot parachuted out of the plane into rebel-held territory, and killed himself with a hand grenade to avoid capture.
Russia's air base and its naval facility in western Syria have recently been under attack.
Two Russian servicemen were reported killed in the mortar shelling of the Hmeimim base on December 31.
The Kremlin denied any of its aircraft were damaged in the attack, but the Russian business daily Kommersant said seven warplanes were damaged beyond repair.
In early January, militants launched a drone attack on Hmeimim as well as a Russian naval base at Tartus.
The Russian military said the attack, which was reported to involve 13 drones, was repelled.
More recently, the United States said that air and artillery strikes launched last month after pro-government forces attacked a base housing U.S.-backed opposition forces and U.S. military advisers killed about 100 of the attackers.
Media outlets, open-source researchers, and relatives and colleagues of Russian mercenary soldiers have said that many Russians -- possibly dozens or hundreds -- may have died in the clash in Syria's Deir al-Zor Province on February 7.
The Russian Foreign Ministry said that "several dozen" citizens of Russia and other former Soviet republics were wounded in the exchange, but insisted that they were not members of the military.