News comes as Russian soldiers reportedly refuse to serve in war-torn Syria
Russia has deployed 28 combat aircraft in Syria, according to US officials.
If verified, the move which was announced on Monday would be the latest in a dramatic build-up of Russian forces and equipment in Syria.
The US has repeatedly said in recent weeks that Russia is developing an air operations base in Latakia, a stronghold of President Bashar Al-Assad.
Security officials confirmed to Reuters on Friday that four jets had already been delivered to a Latakia airbase.
'We don't want to die there'
In spite of the build-up several Russian soldiers have reportedly refused to deploy to Syria, according to a Russian newspaper.
Four soldiers from the southern Russian city of Novorossiysk told online newspaper Gazeta.ru on Friday that a military official said they were scheduled to be deployed to Latakia on 17 September.
The soldiers said they refused to go and subsequently went to a military prosecutor’s office to check the legitimacy of the orders and found that there was no paper work that had been filed, Gazeta.ru reported.
"We don't want to go to Syria, we don't want to die there," one of the soldiers, Alexei, reportedly told Gazeta.
They also filed a complaint with the Council for Civil Society and Human Rights and handed in resignation notices, though it was unclear whether their resignations had been accepted.
The Russian Defence Ministry has denied the Gazeta report and said it was impossible that the soldiers in question, who belong to the Eastern Military District, would be sent to Syria because troops in that area only deploy locally.
Russian embassy shelled
Rebel forces shelled the Russian embassy in Damascus on Sunday, the Russian Foreign Ministry reported.
The ministry said Moscow condemns the "criminal attack" on the Russian diplomatic mission.
"At 09:00 am on 20 September, a mortar shell hit the territory of the Russian embassy in Damascus. The shell was driven deep into the earth and made no damage," the ministry said.
Syria has long been Russia's staunchest ally in the Middle East and has consistently opposed calls for Assad to resign.