The French defense minister said investigators are facing an uphill task in figuring out who was responsible for the slaying of two French journalists in Mali. French Defense Minister Jeav-Yves Le Drian said Wednesday an investigation was under way to determine who killed Radio France International journalists Ghislaine Dupont and Claude Verlon. "This is a crime, a murder" he was quoted by RFI as saying. RFI reports more than 30 suspects have been detained in relation to the investigation. The journalists were found shot to death last weekend after interviewing members of the Tuareg nomadic rebel group in Kidal, near the Malian border with Algeria. The defense minister said Kidal, a Tuareg stronghold, is a "sensitive zone ... meaning that the identification of the murderers is not easy." No group has taken responsibility for the deaths of the two French journalists. The Malian government in January called in support from former colonial power France to help tackle al-Qaida and regional fighters who took control over northern Mali following a 2012 coup.