The Islamic State militants have beheaded a senior leader of Syrian offshoot of Al Qaeda - Jabhat al-Nusra - in Raqqa.

The slain Jabhat al-Nusra leader was identified as Abde Al-Bara Al Iraqi. The execution was carried out on 15 June in al Na'im.

UK-based monitoring group Syrian Observatory For Human Rights, confirming the reports of execution, said it has received a video showing the beheading of the Nusra leader.

In the video, the Nusra leader is shown kneeling on the ground, while an executioner brandishing a sword says that he was being beheaded for opposing and fighting the Isis.

A crowd of onlookers, including young children, witnessed the beheading, SOHR added.

Nusra Front and Islamic State are both Sunni groups that once used to be close allies, but over the year, as Isis grew in prominence inside Syria, both militant groups turned into arch-rivals.

In 2014, Al Qaeda even released an online statement insisting it had no links with the Isis militants. Ayman Mohammed Rabie al-Zawahiri, the current leader of al-Qaeda, even rejected an attempt by the Isis to merge with the Nusra Front, BBC reported.