Over a dozen Islamic State (Isis) fighters have defected from the Sunni terrorist group after realising that it was "not protecting Muslims, but killing them" in Syria.

According to a report published by the International Centre for the Study of Radicalisation and Political Violence (ISCR) at King's College London, an increasing number of former Isis fighters are defecting from the group after realising that the Islamic State is not a protector of Islam.

The report found that many men, who were inspired to join the Isis as they thought it represented a "perfect Islamic State", are now publicly speaking against the terror group and the atrocities on Muslims in Syria and Iraq.

According to the report by ICSR, 58 people who left the Isis have publicly spoken about their defection since January 2014.

Of the 58, the report noted that 17 fighters defected in the last three months--June, July and August--alone. The study says the number represents only a "small fraction" of former fighters, as many are too scared to come forward.

Many found that the Isis was more focussed about power than saving Syrians from the atrocities of its ruler Assad.

The defectors, who were citizens of 17 countries including western Europe and Australia, had left their homes to live in a "promised land". But they were shocked at the mindless killing of Muslims, who were executed after being branded as "spies" and "traitors". They had come for a holy war, a jihad to save Syria and Iraq, but the Isis was all about "brutality", they found.

Unable to stand the random killing of hostages, the mistreatment of local residents and the execution of fighters by their own commanders; many fled to Turkey and are now trying to return to their countries.

Peter R Neumann, professor of security studies and director of ICSR in an edit piece on CNN noted that these "defectors need to be heard". He says that these defectors were not saints or ready to stand in public spotlight but they had one important message for many who aspire to join Isis: "The Islamic State is not protecting Muslims. It is killing them."

Neumann even called on governments and civil society to recognise the defectors and assist them in resettlement. By removing legal disincentives, the government can encourage such defectors to go public against the Isis, he writes.