Ammon News - Reuters - A Syrian rebel commander in a main Islamist brigade was killed and two others were injured in an air strike by President Bashar al-Assad's forces on Aleppo, activists said on Friday, in a setback to rebels defending the city against a loyalist attack.

Aleppo, Syria's commercial hub and most populous city before the uprising against Assad erupted in 2011, has been witnessing heavy fighting since Assad's forces, backed by Shi'ite militia from Iraq and the Lebanese party Hezbollah, launched an offensive two weeks ago to retake rebel-held areas in the city.

The opposition Aleppo News Network said in a statement that the raid on Thursday targeted an army base that rebels had captured, killing commander Youssef al-Abbas of the Qatari-backed al-Tawhid Brigades, one of the biggest armed opposition groups.

Abbas was known by the nom de guerre Abu al-Tayyeb.

Tawhid's leadership was holding a meeting in the base when the raid occurred, the statement said.

It said Tawhid's head, Abdelqader Saleh, was injured and taken to a hospital in Turkey, 45 kms (28 miles) to the north, along with Abdelaziz al-Salameh, another top commander. Both were in good condition, the statement said.

The report could not be independently confirmed.

Video footage taken by activists showed the body of Abu al-Tayyeb after being transported to his hometown of Mareh in the countryside north of Aleppo. His father was shown kissing the body and crying.

Al-Tawhid issued a statement earlier this week, along with other Islamist formations that included al-Nusra Front, an al Qaeda affiliate, declaring a emergency and summoning all fighters to head to the fronts.

Opposition activists said the declaration was an indication of how grave rebels regarded the possibility of Assad, boosted by his Shi'ite militia allies and Iran, wresting back Aleppo.

Hezbollah leader Sayyed Hassan Nasrallah said on Thursday his group will keep fighting in Syria alongside Assad's forces as long as necessary.

The conflict has polarized the Middle East between Sunni Muslim powers such as Turkey and the Gulf Arab states, who support the Sunni rebels, and Shi'ite Iran and its Lebanese ally Hezbollah.

Assad belongs to Syria's Alawite minority, an offshoot of Shi'ite Islam that has controlled the country since the 1960s by dominating the army and security apparatus. Assad's father had forged a now weakened alliance with the Sunni merchant class in Aleppo and Damascus and with Sunni tribes in the east of the country.