PARIS/TIMBUKTU — French authorities detained four people Tuesday in a counter-terrorism operation targeting those suspected of trying to join Islamist extremists abroad. Meanwhile, Tuareg rebels in Mali say they are working with France against 'terrorists.' The raid in the Paris region comes amid fears that European extremists who once joined jihadi groups in Afghanistan or Iraq are now joining radical fighters in the civil war in Syria and the conflict in Mali. The Paris prosecutor's office said the four people were detained in Tuesday's operation as part of an investigation into a French-Malian man arrested around the Mali-Niger border last year. Interior Minister Manuel Valls said the operation targeted those seeking to join foreign fighters in the Mali region, and that French authorities are monitoring several cells or networks suspected of sending fighters abroad. He said a "handful" of French extremists are in the region around Mali, which France fears could become a haven for international terrorists. The French military launched a military intervention in Mali last month targeting Al-Qaeda-linked extremists. The extremists had seized power in the north last year and imposed harsh Islamic rule on residents, and then started advancing toward the capital. Other African countries are also taking part in the military intervention. French authorities fear retaliatory attacks by those linked to the extremists targeted in the Mali operation. French authorities say French extremists are also trying to join radical fighters in Syria, where a melange of anti-government forces is resisting a nearly 2-year-old crackdown by President Bashar Assad's military. France has sided with the Syrian political opposition, saying Assad has lost his legitimacy, but is trying to crack down on any French people who seek to use the war in Syria to push extremist goals. "Several dozen French people or French residents have already gone to Syria, often in groups controlled by Al-Qaeda, and there are also some individuals who want to go to the Sahel (around Mali), so we have to prevent them, arrest them and neutralize them," Valls said. Tuesday's arrests were part of the investigation into Ibrahim Ouattara, a 24-year-old native of the northern Paris suburb of Aubervilliers, the Paris prosecutor's office said. Outtara, a dual French-Malian national, was arrested in November. He has a history of trips to regions where radicals are active, including countries like Yemen and Somalia. Separately, a 27-year-old Frenchman was arrested in August in Niger and has since been handed over to authorities in France. Al-Qaeda in the Islamic Maghreb, or AQIM, is one of three extremist groups that have taken control of the northern half of Mali. The group is made up mainly of foreign fighters. Meanwhile, Secular rebels from Mali's Tuareg people say they have arrested two extremists, including the man blamed for enforcing stoning deaths and amputations in Timbuktu. A statement from the National Movement for the Liberation of Azawad says Mohamed Moussa Ag Mohamed of Ansar Dine and Oumeini Ould Baba Akhmed of the Movement for Unity and Oneness of the Jihad, or MUJAO, were arrested Saturday near Mali's border with Algeria. The NMLA launched a rebellion last year and seized most of northern Mali. They initially fought alongside Ansar Dine and MUJAO but they soon hijacked the Tuareg nationalist uprising. The NMLA said the two men have been interrogated and information shared with French troops who are leading a military intervention in Mali. It said the men are in Kidal, Mali. — Agencies