Syrian rebels in opposition-held areas were engaged in fierce battles with Al-Qaeda-linked elements today in what activists say is growing resistance to the jihadists' brutal grip in many places.
Meanwhile, Doctors Without Borders (MSF) said five of its staffers were taken from a house in the north of the country by an unknown group.
Protesters turned out in rebel areas chanting the strongest slogans yet against the Islamic State of Iraq and the Levant (ISIL), as tensions soar between the Al-Qaeda affiliate and the opposition.
Ammar, an activist on the ground, described today's protests as "the start of the revolution against ISIL."
The Syrian Observatory for Human Rights reported fierce fighting between rebels and ISIL in several flashpoints in Aleppo city and province.
In Aleppo and nearby Idlib, 16 pro-Qaeda fighters were reported killed.
The Britain-based Observatory said a number of battalions united under the name "Army of the Mujahedeen" fought fierce battles against ISIL around Atareb in Aleppo province.
And activists said a number of local rebel groups, including more moderate Islamists, were fighting ISIL.
In Aleppo city, activist Nazeer al-Khatib reported clashes in several neighbourhoods.
The fighting comes two days after ISIL reportedly tortured and murdered Doctor Hussein al-Sleiman, known as Abu Rayyan.
His death was the latest in a string of beatings, kidnappings and killings and has enraged rebels and activists alike.
It prompted protesters to take to the streets of several towns under the slogan: "Friday of the martyr Abu Rayyan."
Amateur video shot in Aleppo city showed protesters chanting: "Free Syrian Army forever! Crush ISIL and Assad!"
A second video from opposition-held Kafr Takharim showed protesters running through the street as gunfire rang out in the background.
The Observatory and activists accused ISIL of firing on the protesters, who were chanting anti-regime slogans as they have every week since the outbreak of an uprising that has killed more than 130,000 people.
