Fighters linked to al-Qaeda have killed two rebel leaders in bombings in Syria, in an apparent shift of tactics to target the command structures of their rivals.

The UK-based Syrian Observatory for Human Rights reported that Adnan Bakour, the leader of Liwa al-Tawhid, was among 26 people killed in a double suicide bombing late on Saturday in Aleppo.

The Islamic State of Iraq and the Levant, which has links with al-Qaeda, said it carried out the attack on Tawhid, a brigade aligned to the Islamic Front coalition, a group fighing the ISIL in Aleppo and beyond.

In another attack late on Saturday in Hama, the leader of the powerful Suqour al-Sham group, Abu Hussein al-Dik, was killed by the ISIL, according to sources spoken to by Al Jazeera.

Charles Lister, of the Brookings Doha Centre, told Al Jazeera that the ISIL was clearly targeting key headquarters, "strategic checkpoints and senior influential commanders" of their rival rebel groups.

The attacks are the latest in weeks of rebel infighting that has pitted a loose alliance of Syrian fighters against al-Qaida linked groups such as the ISIL.

The Observatory also reported that more than 100 people, including 65 civilians, 10 of whom were children, were killed on Saturday when explosive packed barrels were used in an regime air raid in the northern city of Aleppo.

The attack also killed members of Jabhat al-Nusra, al-Qaeda's official affiliate in Syria. The observatory said the Nusra fighters were in their headquarters when it was hit.

Aleppo city has been divided since rebels launched a huge offensive in mid-2012, and heavy fighting between the two sides has left swathes of the city in ruins.

The aerial assault came the day after peace talks in Geneva between the Syrian government and the opposition ended without achieving concrete results.

Regime forces recently launched an offensive on rebel-held areas in the east of the city, with the Syrian defence minister, General Fahd al-Freij, visiting parts of northern Aleppo province on Friday.