It came as the United Nations 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 at least 70 strikes in eastern Deir Ezzor province on Friday, killing at least 36 people, according to the Syrian Observatory for Human Rights.
The Britain-based group said the raids hit several cities and towns in the province, 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 holds the military airport and several smaller areas.
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 a bombing that brought down a Russian passenger jet over Egypt last month, killing all 224 people on board.
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.
According to the Observatory, Russia’s strikes have killed more than 1,300 people since they began, a third of them civilians.
– Lebanon flights rerouted –
The group 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 had been killed, including 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.
And on Saturday, flights in and out of Lebanon were being forced to take longer routes, with some airlines cancelling services, after Moscow requested flights avoid a portion of airspace over the Mediterranean, a Lebanese minister said.
Lebanese Transport Minister Ghazi Zeaiter said Moscow requested “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 of the request, but a Lebanese airport official later said that departing flights would be directed to first fly south over Sidon and Sarafand to “keep them away from the perimeter of the manoeuvres.”
Lebanon’s national carrier Middle East Airlines acknowledged the rerouting in a statement, saying its flights would be mostly on time 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” due to the Russian request, but its Saturday flights were operating regularly.
In France, the president’s office said Francois Hollande would meet British Prime Minister David Cameron on Monday to discuss the Syrian conflict and the threat posed by jihadists.
Hollande is also set to meet next week with US President Barack Obama, Russia’s Vladimir Putin and German Chancellor Angela Merkel in the wake of France’s worst-ever terror attack.
On Friday, the UN Security Council backed a French-drafted measure calling on member states to “take all necessary measures” to fight IS.
The resolution, which does not provide a legal basis for military action, urges countries to “take all necessary measures, in compliance with international law… on the territory under the control of ISIL… in Syria and Iraq“.