Rebel factions who claim to have made gains in Syria's city of Aleppo have come under intense air bombardment from pro-government forces.
The Syrian government released video showing its planes apparently bombing targets in the south-west of the city.
The rebels earlier said they had broken a weeks-long government siege of Aleppo - a claim denied by Damascus.
Some 250,000 people reportedly live in the besieged areas.
On Monday six Russian long-range Tupolev Tu-22M3 bombers dropped fragmentation bombs on so-called Islamic State (IS) targets north-east of Palmyra, an ancient site 211km (131 miles) south of Aleppo, Russia's Defence Ministry said.
The bombers, which flew from Russia, killed many IS militants and destroyed some command posts and heavy weapons, the ministry said on its Facebook page.
Opposition activists said Russian aircraft also took part in the air strikes on Sunday in Aleppo's Ramouseh area. There was no immediate comment from the Russian military.
Air strikes on Aleppo are reported to be continuing on Monday.
Meanwhile, the rebel coalition said it would double the number of fighters to launch a new offensive and retake the whole city.
"We will not rest until we raise the flag of the conquest over Aleppo's citadel," the coalition was quoted as saying.
The Syrian government denies the rebels have made any significant breakthrough, and says the siege remains in place.
However, government forces appear to be redeploying to avoid the rebels making any further gains.
Government forces cut Aleppo's rebel-held areas off in July.
Aleppo was once Syria's commercial capital and also boasted a rich architectural and archaeological heritage.
Much of it has been destroyed or looted during more than five years of war.
Air strike on IS
The Tupolev air strikes on IS destroyed a big insurgent camp and a command post near al-Sukhnah, north-east of Palmyra, the Russian Defence Ministry said.
Near Arak, closer to Palmyra, the bombers destroyed other command posts, an underground ammunition dump, three infantry combat vehicles and 12 pickups equipped with machine guns, the ministry said.
There was no independent verification of the report.
Russian and Syrian government troops pushed IS forces back from Palmyra in late March.