The Nusra Front and its allies launched a multi-pronged offensive early Thursday against Nubl and Zahraa and secured a foothold in the area for the first time, before withdrawing the following day.
The Observatory said that 14 Nusra Front fighters were also killed in the clashes, which saw Al-Qaeda’s affiliate deploy seven tanks.
The offensive failed when several regime airstrikes targeted the jihadis and their allies, it added.
The two towns lie 10 kilometers northeast of Aleppo and have been besieged since the early stages of the insurrection against the government of Syrian President Bashar Assad, and are used to shell nearby rebel-held areas, activists say.
In the city of Aleppo, regime airstrikes targeted several neighborhoods as clashes raged in and around the city, the Observatory and activists said.
Also in Aleppo province, U.S.-led forces launched five airstrikes near the border town of Ain al-Arab, and six in Iraq since Thursday, in their battle against ISIS militants, the American military said.
The strikes in Syria hit several ISIS fighting positions, two tactical units and destroyed a building, according to a statement from the Combined Joint Task Force. The strikes in Iraq hit near Al-Qaim, Al-Asad, Sinjar and Mosul.
ISIS fighters in Ain al-Arab, known as Kobani in Kurdish, have been largely stalled in their monthslong offensive to seize the strategic area. Also, the Observatory reported clashes in rural Hama province, and in rural Deraa province, between regime and rebels that resulted in an unspecified number of casualties.
In Damascus, regime forces detonated a tunnel being used by rebels in the suburb of Jobar, to the east of the capital, and launched airstrikes against the area, the Observatory said.
A bout of winter weather has slowed fighting in a number of parts of the country, but has raised concerned about the plight of refugees and the displaced inside Syria, as the death toll rose. Friday demonstrations were staged in several rebel-held regions to highlight the brutal conditions faced by refugees living in tents.
Pro-opposition media outlets said that up to five deaths were blamed on the cold and the harsh conditions in the rebel-held Damascus suburb of Douma.
Three Syrian refugees from the same family died after a gas leak in their tent in Jordan’s Zaatari refugee camp, local authorities said.
Two children and a woman died of suffocation after a heater leaked, a source from Jordan’s civil defense authority told Turkey’s Anadolu News agency, and the three may have died overnight, with the leak possibly occurring after they had gone to sleep.
The source added that two other refugees had been taken to hospital in a critical condition following the gas leak.
The newborn daughter of Syrian refugees froze to death Thursday in the northern Akkar region of Lebanon, a medical source said.
Two-month-old Salam Barghal became the third Syrian child to die from cold in Lebanon, bringing total fatalities among Syrian refugees in the country due to the snowstorm to five.
At least two people also died in Aleppo Wednesday due to the harsh weather conditions.