Islamic State militants beheaded a Lebanese soldier who was one of 19 captured by hard-line Syrian Islamists when they seized a Lebanese border town for a few days in August, a video posted on social media showed on Saturday.

The soldier, recognizable as Ali al-Sayyed, a Sunni Muslim from north Lebanon, was shown blindfolded with his hands tied behind his back, writhing and kicking the dusty ground while a militant announces he will be killed. Another militant then beheads him.

The Islamic State group, which declared a "caliphate" in June in parts of Iraq and Syria under its control, has been cited as a major security threat by Western governments since posting a video in August of the beheading of U.S journalist James Foley.