* Team of mediators in contact with captors * Kidnappers demand release of militants By Tiemoko Diallo BAMAKO, April 15 (Reuters) - A team of mediators is negotiating the release of four European tourists kidnapped in northeastern Mali in January, a Malian security source said on Wednesday. Al Qaeda's north African wing has said it is holding the two Swiss, one German and one Briton, who were taken from Mali into neighbouring Saharan state Niger. "This team is in contact with the kidnappers and is negotiating the terms of the release of the hostages. The kidnappers' principal demand is that several of their militants are freed from custody," the source said, talking on condition of anonymity. "Negotiations are under way and are progressing." In February, Malian security forces detained an Islamist preacher on suspicion of involvement in the seizure of the hostages. Al Qaeda in the Islamic Maghreb has said it was holding two Canadian diplomats, one of them a U.N. envoy to Niger, as well as the four Europeans. Malian officials initially blamed the Tuareg rebels active in the Sahara for the kidnapping. Military sources say al Qaeda hires them and other armed groups to carry out kidnappings. Several Tuareg rebels were recently released from prison, the Malian security source said, though he did not say whether that was linked to the talks. Mali has tried to negotiate an end to the Tuareg rebellion on its territory, often under Algerian auspices. The Tuareg rebel movement, which is fighting for greater autonomy, spans the border between Mali and Niger. Until recently Niger has dismissed the insurgents as criminals, but earlier this month it had softened its stance, sending its security chief to Libya to try to mediate an end to the insurgency. The January kidnapping was the worst such incident in Mali since Islamist rebels abducted 32 European tourists in 2003. Kidnappers use the size and inhospitability of the Sahara to their advantage in eluding capture, the Malian official said. "All military options are off the table, and besides nobody knows exactly where they are. They are somewhere in this vast desert and they move around a lot," he said. "We've no means of intervening, negotiation is the only option." (Writing by Daniel Magnowski; Editing by David Clarke)
