For the West, meanwhile, the rise of the Islamic State of Iraq and the Levant, as well as another al-Qaida-linked group, the Nusra Front, has been a source of concern, and a major reason that support in Washington and other Western capitals has dwindled in recent months.
Some in northern Syria originally welcomed the Islamic State of Iraq and the Levant for imposing a degree of order on the villages and towns that fell under its control. But the group alienated many by employing tactics deemed brutal even by the standards of Syria’s bloody conflict. Its fighters have beheaded captured government fighters, and kidnapped anti-Assad activists, journalists and civilians seen as critical of its rule.
On Sunday, the violence expanded again, with clashes in the town of Tabaqa in Raqqa province, said Rami Abdurrahman, the director of the Britain-based Syrian Observatory for Human Rights monitoring group.
But much of the heaviest fighting Sunday took place in pockets of Aleppo province.
In the town of Manbij, rebels seized a compound garrisoned by the Islamic State of Iraq and the Levant, activists said. The Observatory said fighters from the al-Qaida-linked group used car bombs, a tactic usually reserved for attacking government forces, for the first time to defend its territory.
In the town of Tal Rafaat north of Aleppo city, insurgents from the Islamic State of Iraq and the Levant ambushed a rebel convoy, killing at least 14 fighters from the Liwa al-Tawhid brigade, which is a member of the Islamic Front, the Observatory said.
The Observatory’s Abdurrahman also reported heavy fighting in the town of Atareb, in several neighborhoods of Aleppo city itself, as well as in areas of Hama and Idlib provinces.
In total, at least 59 fighters — nine of them from the Islamic State of Iraq and the Levant — were killed Sunday, according to the Observatory.