Russia has stepped up its barrage on Syrian rebels with its first submarine-launched cruise missile strikes combined with bombing raids from the air.

The country's Defence Minister Sergei Shoigu confirmed the strikes had been launched from the submarines, progressing on from firing from warships the Caspian Sea.

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

Combined with continuing air strikes, he claimed his military had struck '300 targets of different kinds' in the past three days and helped Syrian special forces recover the black box of a Russian warplane downed by Turkey last month.

Russia has for the first time in the Syrian conflict used submarines (pictured) in the Mediterranean Sea to launch cruise missile strikes on rebels

Some of the missiles launched by the Russians are believed to be able to travel up to 1,500 miles as the country targets rebels as well as ISIS militants in the ongoing civil war

A Russian Tu-22M3 bomber drops bombs on a target in the latest round of air strikes in Syria

Moscow is flexing its military muscle with the latest submarine strikes after having previously fired missiles from warships in the Caspian Sea. Pictured are bombs being released in its latest air strikes

It is believed the cruise missiles, launched from submarines, can travel as far as 1,500 miles at low altitude to attack enemy strongholds.

Shoigu added that Russian strikes launched yesterday had been aimed at 'two terrorist strongholds' around Raqqa, the de facto Syrian capital of the Islamic State jihadist group.

'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.

'The Calibre cruise missile once again showed its effectiveness over long distances.'

Moscow is flexing its military muscle with the latest submarine strikes after having previously fired missiles from warships in the Caspian Sea.

An unnamed source told Interfax news agency earlier that a Russian submarine was approaching Syria's Mediterranean coast to launch cruise missiles toward to war-torn country.

President Vladimir Putin said the Caliber cruise 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'.

Shoigu said Moscow had warned Israel and the United States - conducting their own bombing campaigns in Syria - that the Russian military would be conducting the submarine strikes.

Shoigu added that Russian military jets had conducted 600 combat sorties and destroyed '300 targets of different kinds' in the past three days.

Meanwhile it has emerged the number of foreign fighters joining ISIS and other extremist groups in Iraq and Syria has more than doubled since last year to at least 27,000, a report by an intelligence consultancy has revealed.

Moscow is flexing its military muscle with the latest submarine strikes after having previously fired missiles from warships in the Caspian Sea

Oil infrastructure, ammunition depots and a mine-making factory were hit in the latest Russian attacks

Russian strikes launched yesterday had been aimed at 'two terrorist strongholds' around Raqqa

This screenshot shows how the target is locked in and the missile lands during the targeted strikes

The Russian government has said the military would be continuing to conduct submarine strikes

The figures, compiled by The Soufan Group, indicate that efforts by countries around the world to stem the flow of foreign fighters to the region and blunt the appeal of violent organisations appear to have made little impact.

'The foreign fighter phenomenon in Iraq and Syria is truly global,' the New York-based security consultancy's report said.

'The Islamic State has seen success beyond the dreams of other terrorist groups that now appear conventional and even old-fashioned, such as Al Qaeda.

'It has energised tens of thousands of people to join it, and inspired many more to support it.'