The Britain-based Syrian Observatory of Human Rights and two other monitoring groups said Friday that the air raids since Thursday night had the heaviest since IS captured a Jordanian pilot on December 24.
At least 13 coalition strikes had occurred from Thursday into Friday said the anti-IS activist group which calls itself Raqqa is Silently Being Slaughtered.
Raqqa (pictured in a November photo) is the IS' de facto capital in northeastern Syria, part of a swathe of territory seized by the jihadists across Syrian and northwestern Iraq last year in a bid to establish an Islamic caliphate.
The US-coalition's Combined Joint Task Force said its aircraft had destroyed IS vehicles, and fighting positions near Raqqa, al-Hasakah and Kobani.
The news agency Associated Press said Friday it had information suggesting that a Saudi cleric aligned with IS and named as Othman al-Nazeh al-Assiri had been killed during the airstrikes on Kobani.
The town near Syria's border with southern Turkey has for months been the scene of intense clashes between IS jihadis and Kurdish gunmen.
Further bloodshed in Aleppo
The Syrian Observatory said Syrian rebel fire on Syrian government-controlled parts of Syria's northern city of Aleppo have claimed the lives of at least 19 people.
Those killed included at least five children, three of whom were killed with their mother when a rocket hit the car in which they were travelling.
Thursday's rocket attack on Aleppo's west has also left at least 32 people wounded.
Three other people, including a pregnant woman, had been killed by a ground-to-ground missile fired by government forces at a rebel district in eastern Aleppo, the Observatory added.
Aleppo, once Syria's economic hub, has been ravaged by fighting that begin in 2012.
Economic hub now divided
The city is divided, with government forces controlling its western areas and rebels control the east.
More than 200,000 people have been killed in Syria since March 2011 when Syria's complex conflict began. Last year was the deadliest so far.
ipj/rc(AFP, Reuters, AP)