The United Nations, meanwhile, passed a motion calling for action against IS, a week after 130 people were killed in Paris, sparking international condemnation and fears of similar attacks elsewhere in Europe.
Russian and Syrian warplanes carried out more than 70 strikes in eastern Deir Ezzor province on Friday, killing at least 36 people including 10 children, the Syrian Observatory for Human Rights said.
The Britain-based group said the raids hit several cities and towns as well as three oilfields, and were the heaviest bombardment of the region since the conflict began in March 2011.
Most of Deir Ezzor province, including large parts of its capital, is held by IS.
The regime still controls the military airport and several smaller areas.
On Saturday, fighting raged between IS and regime forces around the airport, a day after clashes killed 30 people, 22 of them IS militants, according to the Observatory.
Russia began its bombing campaign in support of President Bashar al-Assad on September 30, and pledged to step up the strikes after IS claimed that a bomb downed a Russian passenger jet over Egypt last month, killing all 224 people on board.
Rebels capture IS villages
On Friday, Russia said it had fired cruise missiles from warships in the Caspian Sea and claimed to have killed 600 fighters in recent strikes.
The Observatory says Russian strikes have killed more than 1,300 people since they began, a third of them civilians.
It says 381 IS fighters have been killed in the strikes, along with 547 rebels from other groups including Al-Qaeda affiliate Al-Nusra Front.
It said 403 civilians have been killed, among them 97 children.
Russia’s military involvement in Syria has stirred tensions with Turkey, which backs the uprising against Assad and has accused Moscow of failing to respect its border and airspace in the campaign.
The Turkish state-run Anatolia news agency reported Saturday that Syrian Turkmen rebels seized from IS the villages of Harjaleh and Dalha in northern Aleppo province near the Turkish border.
It said 70 IS jihadists were killed in the battle for the villages which the Turkmen captured with air support from American and Turkish warplanes.
Turkish officials have said a major joint air operation against IS with the United States was planned, with Turkmen forces fighting on the ground.
They said the aim is to clear of jihadists a 98-kilometre (61-mile) stretch of Syria’s northern border with Turkey still controlled by IS.
Lebanon flights rerouted
On Saturday, flights in and out of Lebanon were rerouted and some airlines cancelled services after Moscow requested they avoid an area over the eastern Mediterranean.
Lebanese Transport Minister Ghazi Zeaiter said Moscow asked “that planes leaving Beirut airport towards the west avoid overflying an area in Mediterranean territorial waters because of manoeuvres on Saturday, Sunday and Monday”.
There was no confirmation from Moscow, but a Lebanese airport official said departing flights would be directed south over Sidon and Sarafand to “keep them away from the perimeter of the manoeuvres”.
Lebanon’s national carrier Middle East Airlines said most of its flights would be on schedule but “some flights to the Gulf and the Middle East region might take (a) longer time due to a slight change in airways”.
Kuwait Airways said it was suspending its Beirut flights “as a precautionary measure” but most other flights were arriving and leaving normally.
Turkey’s Dogan news agency said two Turkish Airlines services to Beirut on Friday night were cancelled for “security reasons” after the Russian request, but its Saturday flights were operating normally.
In France, President Francois Hollande’s office said he and British Prime Minister David Cameron would meet Monday to discuss the Syrian conflict and the threat posed by jihadists.
Hollande is also set to meet next week US President Barack Obama, Russia’s Vladimir Putin and German Chancellor Angela Merkel in the wake of France’s worst-ever terror attacks.
The UN Security Council unanimously approved a resolution Friday authorising countries to “take all necessary measures” to fight IS in Syria and Iraq.
The resolution, drafted by France, does not provide a legal basis for military action but urges countries to coordinate their efforts to prevent IS “terrorist attacks”.