The defence ministry said its jets had destroyed an IS ammunition depot and control centres.
However, the areas reportedly attacked appeared to be held by groups opposed to IS and the Syrian government.
The US and its allies fears the strikes have been targeting non-IS opponents of Russia’s ally, Syrian President Bashar al-Assad – a claim denied by Moscow.
The latest attacks reportedly hit sites in the north-west held by the Army of Conquest rebel alliance, as well as areas in Homs and Hama provinces.
They reportedly hit areas near the strategic town of Jisr al-Shughour, as well as areas in Idlib province and Hama province further south, according to Lebanon’s al-Mayadeen TV.
Rebel activists also reported strikes at Ghantu in Homs province, close to where some of Wednesday’s strikes hit.
Russia said that it had hit 12 IS positions in the past 24 hours, although this cannot be independently verified.
The Syrian government’s army may not be what it was, but in local terms it is still a force to be reckoned with.
Bolstered with new Russian equipment and now backed by Russian air power, it could hold its own against most of the opposition forces.
Russia does not have the elaborate intelligence gathering panoply of the US. But much of its targeting will be based upon tactical intelligence obtained from Syrian units on the ground.
This then is the key to Russia’s strategy. It is to consolidate the Assad regime, to relieve the pressure points and to ensure that its ally remains a factor in any future diplomatic settlement.
To this end – and there are strong indications of this even from Russia’s initial air strikes – Moscow will hit any opponents of the Syrian regime where necessary.
The Army of Conquest (Jaysh al-Fatah) alliance had made advances in the north-west in recent months, taking Idlib and Jisr al-Shughour from pro-government forces.
The alliance includes the al-Nusra Front, al-Qaeda’s affiliate in Syria, and the hard-line Islamist group Ahrar al-Sham, as well as several more moderate Islamist groups.
All are opposed to IS and have fought bloody battles with the jihadist group.
More than 50 planes and helicopters are involved in the Russian military operation in Syria, Russia’s defence ministry said.
The US, which is targeting IS with air strikes in both Syria and Iraq, says it was informed about Russia’s air strikes only an hour before they began on Wednesday.
Nato said there had been little co-ordination by Russia with US-led forces.
The French defence minister said the strikes had not targeted IS, while US Defence Secretary Ashton Carter said Russia’s approach was “tantamount to pouring gasoline on the fire” and “doomed to fail” because of the breadth of Syrian opposition to Mr Assad.
But Russian Foreign Minister Sergei Lavrov said his government stood by its targets.
“The rumours that the target of these air strikes was not IS positions are unfounded,” he said. “Talk began that civilians were hurt by air strikes. We have no such data.”
Mr Lavrov said there was a need to “establish channels of communication to avoid any unintended incidents”. His US counterpart, John Kerry, said talks would be held “as soon as possible,” maybe as early as Thursday.
More than 250,000 Syrians have been killed and a million injured in four-and-a-half years of armed conflict, which began with anti-government protests before escalating into a full-scale civil war.
More than 11 million others have been forced from their homes, four million of them abroad, as forces loyal to President Assad and those opposed to his rule battle each other – as well as jihadist militants from IS and other groups. Growing numbers of refugees are going to Europe.
Regional and world powers have also been drawn into the conflict. Iran and Russia, along with Lebanon’s Hezbollah movement, are propping up the Alawite-led government. Turkey, Saudi Arabia and Qatar are backing the Sunni-dominated opposition, along with the US, UK and France.