Al Qaeda’s affiliate in North Africa is the militant organisation’s richest faction and the dominant Islamist force among those controlling northern Mali, the head of the U.S. military’s Africa Command (AFRICOM) said on Thursday.General Carter Ham said the international community and the Malian government now faced a complex challenge to try to deal with the strengthened presence in Mali’s largely desert north of al Qaeda in the Islamic Maghreb (AQIM), the militant group’s North African franchise.Mali, for a long time seen as a stable nation in an often turbulent West African region, imploded in the space of a few weeks after a March 22 coup sowed confusion and allowed a mix of Tuareg separatists and Islamist rebels to occupy the northern two-thirds of the country.Over recent weeks, the Islamists, including AQIM fighters, have gained control of the vast area, creating what African and Western leaders are calling a "terrorist haven” that they say threatens both regional and international security.African leaders and Western governments including the United States and France, the former colonial power in the region, have been discussing the idea of a Western-backed African military intervention force going in to try to expel the rebels from the north and reunite divided Mali.Ham said the groups now controlling Mali’s north were boosted by the spillover of arms and fighters from Libya’s conflict last year. But he criticised as "ineffective” previous efforts to tackle AQIM in northern Mali, where its members have held kidnapped foreigners for multi-million-dollar ransoms."We - the international community, the Malian government - missed an opportunity to deal with AQIM when they were weak. Now the situation is much more difficult and it will take greater effort by the international community and certainly by a new Malian government,” Ham told reporters in Senegal.The U.S. general said relationships between the various Islamist groups in northern Mali were complex and that it was not clear if they were aligned on an ideological or a purely opportunistic basis.