BEIRUT: Dozens of people have been killed in 24 hours of clashes in northern Syria between regime forces and jihadist militants, the Syrian Observatory for Human Rights said on Friday.
The watchdog reported on Thursday that the Islamic State (IS) group had launched multiple attacks on government-held territory across north and northeast Syria.
The Observatory said it was the first time that IS, accused by rival rebel groups of focusing its formidable firepower more on them than on the Damascus regime, had launched such coordinated assaults on army positions.
The jihadists went on the offensive near the main northern city of Aleppo, in Hasakeh province in the northeast and in Raqa province around their Euphrates valley stronghold, the Observatory said.
The IS, which in June announced a "caliphate" straddling Syria and Iraq, controls swathes of both countries and is seeking to seize more territory.
In Hasakeh province, "at least 17 IS jihadists were killed on Thursday ... in clashes and in regime bombardment," said the Britain-based Observatory which relies on activists and medics on the ground for its reports.
In the provincial capital of the same name, four suicide bombers launched an attack inside the local headquarters of President Bashar al-Assad's Baath party, which was followed by clashes inside the building.
The Observatory said 12 people, including Baath members and guards, were killed. Among the dead was "a Baathist who was decapitated with a sharp instrument".
South of Hasakeh city, 11 soldiers were killed in an IS attack on a regime position and 17 jihadists were killed, it said.
"Regime bombardment forced the IS to withdraw overnight," Observatory chief Rami Abdel Rahman said on Friday.
In Raqa province, which is mainly held by IS, the jihadists attacked two positions of the army's 17th Division, sparking fighting that left dozens of dead and wounded, the Observatory said.
In one attack, two suicide bombers -- one a Saudi -- blew up trucks packed with explosives.
"At least six soldiers, one an officer, were decapitated and eight jihadists were killed," said the Observatory.
IS posted photographs on its Twitter account of six decapitated corpses that it said were soldiers of the 17th Division.
"The IS wants to 'clean' the province of any army presence," Abdel Rahman said.
East of Aleppo, the jihadists attacked the Kuwayris airbase, sparking fierce fighting on Thursday that has since died down, the Observatory said.
The more than three-year conflict in Syria is becoming increasingly complex as the IS battles regime forces, mainstream rebels, its rivals and former allies the Al-Qaeda-linked Al-Nusra Front, and Kurdish separatists.
IS jihadists are seeking to expand the fiefdom they have carved out along the Euphrates Valley by taking the battle to neighbouring government-held areas after routing rival rebels in Deir Ezzor province in Syria's east earlier this year. (AFP)