Twenty members of the Islamic State (IS) were killed in Syrian air force raids on Wednesday against the jihadists' bastion in Raqa, the Syrian Observatory for Human Rights said.
The report comes after Syrian rebels killed at least 14 people overnight, among them women, in the village of Khatab in central province of Hama, state media and the Observatory said.
"At least 20 members of IS were killed and others were injured in air strikes... targeting an IS training base in Raqa," said the Observatory.
The strikes also destroyed 14 of IS' military vehicles, the Observatory added.
On June 29, IS declared the establishment of a "caliphate", referring to an Islamic system of rule that was abolished nearly 100 years ago.
Its jihadists are firmly in control of Raqa, their stronghold, and have secured large swathes of territory in eastern Syria and in neighbouring Iraq.
While some in the Syrian opposition initially welcomed IS -- formerly known as the Islamic State of Iraq and the Levant (ISIL) -- among their ranks, viewing it as a potential ally, its abuses and quest for control turned the rebels against them.
Rebels have been fighting IS since January.
The Syrian regime of President Bashar al-Assad, for its part, has escalated its attacks against IS positions since the group spearheaded a Sunni militant offensive in neighbouring Iraq.
Syrian Kurds, for their part, have been fighting IS since 2013.
On Wednesday, a Tunisian jihadist carried out a suicide car bomb attack in the Syrian Kurdish town of Ain Eissa, killing four Kurdish fighters.
The attack comes a day after 22 IS jihadists and 18 members of the Kurdish People's Protection Units (YPG) were killed in fighting that continued Wednesday in a Kurdish area of Aleppo province.
The reports come hours after Syrian state television said rebels carried out a "massacre" that included women and children, while the Observatory said seven men and seven women had been "executed" by rebel fighters.
The Observatory said the rebels accused the residents of Khatab village of "collaboration with the criminal regime", and executed the 14.
Meanwhile, in northern Syria's Aleppo, four people, among them a media activist, were killed and dozens of others injured in air raids on rebel-held areas, the Observatory said.
Aleppo has come under a massive aerial offensive since December.
According to the Observatory, by May some 2,000 civilians including 500 children had been killed in the daily air strikes, which rights groups have condemned as a "war crime" for failing to discriminate between military and civilian targets.
Rebel fighters also launched mortars against regime-held areas of divided Aleppo, killing three people, according to the Observatory.
More than 162,000 people have been killed since Syria's conflict erupted in March 2011.
It began when protesters took up arms after being fired on by government troops during peaceful anti-regime demonstrations.