Russia flexed its military muscles as it launched strikes in Syria for the first time from a submarine stationed in the Mediterranean, ratcheting up its bombing campaign in the war-torn country.

The strikes came with Syria's splintered opposition due to begin Saudi-organised talks in Riyadh on Wednesday for difficult discussions on forming a united front in potential talks with President Bashar al-Assad to end the country's years-long conflict.

Moscow's latest strikes hit "300 targets of different kinds" in the past three days and helped Syrian special forces recover the black box of the Russian warplane downed by Turkey last month, Defence Minister Sergei Shoigu said.

"We used Calibre cruise missiles from the (Kilo-class) Rostov-on-Don submarine from the Mediterranean Sea," Shoigu told President Vladimir Putin during an encounter broadcast on state television.

"As a result of the successful launches by the aviation and submarine fleet, all targets were destroyed," Shoigu said, adding that oil infrastructure, ammunition depots and a mine-making factory had been hit in the strikes.

Russia launched a bombing campaign in Syria on September 30, saying it needed to target Islamic State (IS) jihadists -- but the West has accused Moscow of seeking to prop up Assad's regime and hitting moderate rebels.

Moscow stepped up strikes against IS after the group claimed responsibility for the bombing of a Russian passenger plane over Egypt's Sinai Peninsula in October, killing all 224 people on board.

Russia is once again flaunting its military might after having previously fired missiles from warships in the Caspian Sea.

Russia launched a missile attack on #ISIL in Syria from a submarine in the Mediterranean for the first time https://t.co/ek6kbpU5AE — CCTVNEWS (@cctvnews) December 9, 2015

The Russian defence ministry said it had upped the intensity of its strikes in Syria since Saturday, dropping 1,920 bombs over the past four days.

Putin said Tuesday that the Calibre missiles launched from the submarine could be equipped with nuclear warheads -- but said he hoped they would "never be needed in the fight against terrorism".

The latest strikes came ahead of talks in Riyadh which mark the first time representatives of some of Syria's various political and armed opposition factions will come together since the outbreak of the country's conflict in March 2011.

The goal is to form a unified bloc for talks with Assad that world powers hope can be held before January 1.