A jihadist with family ties to the inner circle of Islamic State’s leader, Abu Bakr al Baghdadi, has been arrested in western Turkey preparing to be smuggled into Greece.

Kasir al Haddawi, a Syrian national, was one of four Isis suspects detained in a major police operation in the coastal city of Izmir this morning; he had been planning to take a migrant boat to Greece. Authorities said that the arrests may have halted a future attack in the heart of Europe.

A top ISIS commander in the province of Deir Ezzor in Syria, Haddawni is thought to have been responsible for the massacre of 700 civilians in December as the group’s caliphate crumbled.