At least 36 people were killed Friday in air strikes by Russian and Syrian jets on Islamic State-controlled Deir Ezzor province, a monitor said, describing them as the heaviest in the region since the start of the war.
Russia pounded the jihadist group in Syria, firing cruise missiles from warships in the Caspian Sea after President Vladimir Putin vowed retaliation for a bombing that brought down a Russian airliner in Egypt last month.
At the United Nations, member states backed a motion calling for action against IS a week after 130 people were killed in Paris, the worst such attack on French soil also claimed by the jihadist group based in Syria and Iraq.
"At least 36 people were killed and dozens more injured in more than 70 raids carried out by Russian and Syrian planes against several districts in Deir Ezzor," Rami Abdel Rahman of the Syrian Observatory for Human Rights monitoring group told AFP.
He described the raids, which targeted several large cities and smaller towns in the province and three oil fields, as "the worst bombardment of the region since the start of the uprising in 2011".
French soldiers prepare a Rafale fighter jet at a military base at an undisclosed location in the Gulf on November 17, 2015, as the French army conducts operations against the Islamic State group in Syria and Iraq.
The province and most of the provincial capital is held by Islamic State militants, with the exception of the military airport and a few areas controlled by the regime.
Russia began bombing in Syria in September at the request of its longstanding ally President Bashar al-Assad, while a US-led coalition is conducting its own air campaign against IS.
Putin this week pledged to hunt down and "punish" those behind a bombing that brought down a passenger jet in Egypt last month, killing all 224 people on board in an attack claimed by IS.
Moscow claimed to have killed more than 600 fighters after hitting seven targets in the Raqa, Idlib and Aleppo provinces, Defence Minister Sergei Shoigu was quoted as saying by Russian news agencies.
It was the second time that warships have been used since the start of the bombing campaign on September 30.
'From Paris with love'
Russian television showed a man scrawling "For our people!" and "For Paris!" in black pen on bombs minutes before a warplane was set to take off from the country's airbase in Syria.
Unverified images circulated on the Internet of Syria-bound US missiles bearing the handwritten inscription "From Paris with love".
Lebanon said Friday it was preparing to re-route flights from Beirut airport after Russia requested they avoid an area over the eastern Mediterranean because of three days of military manoeuvres.
A video grab made on November 20, 2015 shows an image taken from footage made available on the Russian Defence Ministry's official website on November 20, 2015.
Putin praised the Russian operation in Syria -- its largest foreign intervention outside the former Soviet Union since it occupied Afghanistan in 1979 -- but said it was "still not sufficient" to wipe out the jihadists in the country.
The UN Security Council on Friday backed a French-drafted measure calling on member states to "take all necessary measures" to fight IS, a week after the Paris attack.
The resolution, which does not provide a legal basis for military action, urges those countries which can to "take all necessary measures, in compliance with international law... on the territory under the control of ISIL... in Syria and Iraq".
The US-led coalition fighting IS said Monday it had destroyed 116 fuel trucks used by the jihadists in eastern Syria, in one of the largest raids in weeks.
IS reportedly makes millions of dollars in revenue from oil fields under its control, and the coalition has regularly targeted oil infrastructure held by the group.
An investigation by British newspaper The Financial Times last month estimated the jihadists reap some $1.5 million a day from oil, based on the price of $45 a barrel.