The French teacher, who had recently shown students insulting cartoons of the Prophet Mohammad (PBUH) was beheaded outside his school on Friday.
The 18-year-old killer, who was born in Moscow but has Chechen roots, was killed by police. His family arrived in France when he was a child, investigators said. Police were questioning his parents, grandfather and 17-year-old brother and detained another five including the father of a pupil at the school and an acquaintance of his known to the intelligence services.
Ali al-Qaradaghi, the IUMS secretary-general, in a Facebook post denounced the killing of the teacher.
He also wondered why the French government refuses to respect the sanctities of religions and pass laws that ban desecrating such sanctities.