Kazakhstan’s state security service has detained several people suspected of stealing oil and fuel from a refinery and being linked to radical Islamists, it said on Wednesday.

The large-scale raid took place in the city of Aktobe, the National Security Committee said in a statement, the site of a deadly Islamist attack last June in which 25 people, including 18 attackers, were killed.

The security service said it had seized several tanker trucks loaded with oil and oil products. Aktobe is home to a small refinery which processes about 300,000 tonnes of oil a year and there are several oil fields in the vicinity.

Along with the suspected thieves, security forces have detained “several members of an organized criminal group made up of followers of radical Salafism,” the security service said, referring to an ultra-conservative school of Islam.

It said the detained Islamists are suspected of having provided protection to the oil thieves.

The June attack targeted a national guard base and firearms shops in Aktobe. It was the deadliest incident of its kind since the country became independent of the Soviet Union in 1991.

Last month, a local court sentenced most of the surviving attackers – described by prosecutors as Islamic State sympathizers – to life in prison.