At a conference of coalition members tasked with fighting ISIS in Rome yesterday, Secretary of State John Kerry said members of the terrorist organization are not Muslims but apostates of Islam.

“Daesh [ISIS] is in fact nothing more than a mixture of killers, of kidnappers, of criminals, of thugs, of adventurers, of smugglers and thieves,” Kerry said. “And they are also above all apostates, people who have hijacked a great religion and lie about its real meaning and lie about its purpose and deceive people in order to fight for their purposes.”

Apostate, according to The Washington Post, has traditionally been used to describe an individual or, in the plural, a group who abandoned or renounced their religion. Kerry’s application of the term to ISIS is somewhat ironic considering the terrorist organization has justified its attacks on other Muslims by claiming the victims were apostates themselves, which suggests ISIS militants are active participants in the Muslim faith.

This is not the first time Kerry has referred to ISIS as apostate. At the Saban Forum in December, Kerry said the terrorist organization is “a mixture of killers and kidnappers, smugglers, thieves, and apostates who have hijacked a religion and combined a medieval thinking with modern weapons to wage an especially savage brand of war.”

Cairo’s Al-Azhar, the world’s preeminent authority on the Sunni branch of Islam, has refused to call ISIS an apostate group, since ISIS fighters do believe and practice Islam, even though their understanding of the religion is flawed in his opining, CNS News reports.

Social media users have attacked Kerry’s usage of the term as untrue and Kerry lacks any authority on Islam:

Who is Kerry to determine who is an apostate of Islam? https://t.co/k3WknobM5v

— Chris Bowers (@chrisbowers) February 4, 2016

I am actually apostate. Kerry's use doesn't make sense. https://t.co/TYddSx1M8G

— Alison (@tikidaisy) February 4, 2016

So Kerry, who isn't even a faithful Catholic, is somehow able to pass judgement on who is an apostate of Islam: https://t.co/K6kLHLrSpw

— Adam Cassandra (@adamcassandra) February 3, 2016

Did John Kerry really say that ISIS members are apostate?

— Yunus (@Unenemous) February 3, 2016

@AdamPlatt1999 @shadihamid How is a non-Muslim calling any Muslim an apostate? Not sure John Kerry qualifies as an expert in Islam.

— Jeremy (@jthurgood1) December 15, 2015