Mali's transitional government has rejected rebels' claims the north will become an independent state.
The Tuareg rebels and Islamist militants fought side-by-side in a fast-moving offensive to seize the north, following a March 22 military coup in Bamako.
Initially, the Tuareg rebels and Islamist group had separate goals. The Tuaregs sought to create an independent secular state of Azawad, while Ansar Dine wanted to impose Sharia across the entire country.
Sect members have started introducing hardline Islamic law in Gao and Timbuktu.
Residents in the region, who are accustomed to a moderate forms of Islam, have resisted the new measures.