Syrian government troops have launched a ground offensive in the country's central region under cover of Russian airstrikes.

And in the first salvo from the sea, Russian warships fired missiles into Syria, with Moscow saying they were targeting militants.

The latest developments - exactly a week after Russia began launching airstrikes in Syria - add a new layer to the fray in the complex war that has torn the Middle East country apart since 2011.

Moscow has mainly targeted central and north-western Syria, strategic regions that are the gateway to president Bashar Assad's strongholds in Damascus, and along the Mediterranean coast.

But the strikes appear to have given Assad new confidence to try to retake some lost ground.

According to Syrian officials, the government push is concentrated in the adjacent provinces of Hama and Idlib where rebels have been advancing in the past months.

Islamic State (IS) is not present in the areas where the fighting is under way.

The offensive in central Syria and the ensuing clashes with militants, including al Qaida's Syrian branch, was the first major ground fighting since Moscow began launching air raids in Syria last week.

The Russian airstrikes appear to have emboldened Syrian troops to launch the ground push after suffering a string of setbacks in north-western Syria over the past few months.

In Moscow, Russian defence minister Sergei Shoigu said Russia is using warships in the Caspian Sea to target IS in Syria.

Mr Shoigu told President Vladimir Putin in televised remarks that Russia on Wednesday morning carried out 26 missile strikes from four warships of its Caspian Sea flotilla. Mr Shoigu insisted the operation destroyed all the targets and did not launch any strikes upon civilian areas.

Mr Shoigu also said Russia has carried out 112 airstrikes on IS positions since its operation began on September 30.

The Britain-based Syrian Observatory for Human Rights said a government offensive began on four fronts early on Wednesday in the north-western provinces of Idlib and neighbouring Hama.

Observatory director Rami Abdurrahman described it as "the most intense fighting in months".

In Syria, the leader of a US-backed rebel group, Tajammu Alezzah confirmed the ground offensive, claiming there were Russian and Iranian soldiers in the operation.

The observatory, which has a network of activists on the ground, said the main launching point for government forces is the town of Morek on the highway that links the capital, Damascus, with the northern city of Aleppo, Syria's largest city and former commercial centre. Rebels have controlled areas on the highway since 2012.

The Local Co-ordination Committees, another activist group, said rebels were able to destroy two tanks and an armoured personnel carrier in northern parts of Hama province near Idlib.

The observatory said two helicopters - believed to be Russian - were seen flying at low altitude in Morek. It added that militants opened fire at the helicopters without striking them. It was not immediately clear if the pilots were Russian or Syrian. The Syrian military has Russian-made helicopters in its air force.

In Turkey, prime minister Ahmet Davutoglu renewed criticism of Russia's airstrikes in Syria, insisting they were mainly targeting the moderate Syrian opposition and therefore helping strengthen IS.