The 15-minute film, entitled ''No Protection Except by Emaan or Amaan 1 - Mpeketoni", which was posted on Tuesday shows footage of the militants shooting residents and setting fire to buildings in June 2014.
Anti-persecution group Release International has said it believes the group is directly targeting Christians, according to one eyewitness to the attack who spoke to Release, Paul said: "They would force the women and the children to watch as they slowly cut their necks using very sharp knives. A few pastors actually abandoned their churches and fled and they have never come back again."
The late Sheikh Aboud Rogo, a Kenyan radical Islamist cleric shot by Kenya security forces in 2012, also appears in the video giving a lecture in Swahili language in which he urged the youths to fight against what he called ''kufaar'' (Non-Muslims).
Al-Shabaab has claimed it carried out the attack in order to take revenge on Kenya for the presence of its troops in Somalia, where they are battling the militants, as well as for the killing of radical clerics linked to al-Shabab in the port city of Mombasa.
Release International's report by Andrew Boyd on the rise of attacks against Christians in Kenya by Islamic extremists:
