An al-Qaeda affiliated rebel group in Syria is reported to have asked for forgiveness after beheading a fellow rebel in a case of mistaken identity.

A video recently posted online showed members of the Islamic State of Iraq and the Levant (ISIS) brandishing the severed, bearded head of a man, they said was an Iraqi Shia caught fighting on the government side.

But other rebel fighters watching the video recognized the man and said he was one of their commanders.

In a separate development, activists said a senior figure in another Islamist rebel group had been killed in an air strike near Aleppo.

Youssef al-Abbas of Liwa al-Tawhid was reportedly meeting the brigade's leader, Abdul Qader Saleh, and another senior figure, Abdul al-Aziz Salameh, at a rebel-held air base on Thursday when he was killed.

It said Youssef al-Abbas, also known as Abu al-Tayyeb, was Liwa al-Tawhid's intelligence chief, but the UK-based Syrian Observatory for Human Rights described him as the group's financial officer.

Mr. Saleh and Mr. Salameh were wounded in the attack and report said that they were taken to a hospital in Turkey and were in a good condition.

Video footage posted online by activists purportedly showed Abu al-Tayyeb's body being transported to his hometown of Mareh.