Islamist Rebels seize power in Gao mist forces in northern Mali are reported to have seized the town of Gao after clashes with Tuareg-led rebels.
Residents say the Islamists have taken over buildings occupied by the Tuaregs - including their headquarters - and raised their black flag.
At least 20 people have been killed and witnesses say many Tuaregs have fled.
Tension has been growing since the Tuaregs and Islamists jointly took control of northern Mali following a coup earlier this year.
The fighting in Gao followed a day of protest after a local official was killed on Monday.
Residents said heavy weapons were being used.
A doctor in Gao told the BBC that most of the people who were killed and injured seemed to have been armed, but a number of civilians had also been caught in the fighting.
In March, the Islamists and the secular Tuareg National Movement for the Liberation of Azawad (MNLA) advanced together through northern Mali after the government was overthrown.
BBC West Africa correspondent Thomas Fessy says they proved unable to reach an agreement after they took control of the region, prompting fears of renewed violence between the different factions.
Last month the secular MNLA agreed to Islamist demands to have Islamic Sharia law imposed across northern Mali.
More than 300,000 people have fled northern Mali since the rebels took the territory in the days following the 22 March coup.