The Britain-based group said the raids hit several cities and towns as well as three oilfields, in the heaviest bombardment there since the conflict began in March 2011.
Most of the province, including large parts of its capital, is held by IS.
The regime still controls the military airport and several smaller areas.
Fighting raged Saturday 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, along with 547 rebels from other groups including Al-Qaeda affiliate Al-Nusra Front.
Of the 403 civilians killed, 97 were 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.
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 air operation with the US against IS was planned, with Turkmen forces fighting on the ground.
They said the aim is to clear jihadists from a 98-kilometre (61-mile) stretch of Syria's northern border with Turkey.
In other violence, aid group Doctors Without Borders said Saturday that bombardment of areas in Eastern Ghouta, where it provides assistance, had killed eight people over the previous two days.
- 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.
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".
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".
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 were cancelled Friday night for "security reasons", but its Saturday flights were operating normally.
Meanwhile, French President Francois Hollande's office said he and British Prime Minister David Cameron would meet Monday to discuss the war 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.
US Secretary of State John Kerry was also due in Abu Dhabi next week for talks on a number of issues "with a focus on Syria", his spokesman said Saturday.
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".