PARIS (Reuters) - French authorities are holding a former Iraqi refugee in custody on suspicions he committed war crimes as a local leader of Islamic State, the Paris prosecutor’s office said on Thursday.

The man, whose identity has not been made public, was also put under formal investigation for criminal association in relation to a terrorist undertaking and joining an armed group seeking to commit war crimes, the prosecutor’s office said.

French TV channel TF1 first reported the news and identified the suspect as Ahmed H., aged 33.

Iraqi authorities suspect him of being a former local ruler of Islamic State over the regions of Tikrit and Samarra, about 100 km (60 miles) north of Baghdad, according to sources close to the investigation.

Islamic State said it killed 1,700 prisoners from the Iraqi army detachment at Camp Speicher in June 2014. The detained man is suspected of having participated in the massacre, according to the same sources.

More than 240 people have been killed since early 2015 in France in attacks carried out by Islamist militants or individuals inspired by Islamist groups.