Boko Haram militants have joined the armed rebellion in northern Mali, security officials said.
Tuaregs and radical Islamist groups have occupied several cities in the north of Mali following a two-month rebellion.
The armed militias made significant advances after the government was overthrown by a military junta.
Last week, Islamists stormed the Algerian embassy in Gao, taking seven Algerian diplomats as hostages. It is not clear whether they have now been freed.
Security sources said the group was led by at least 100 Boko Haram fighters.
"There are a good 100 Boko Haram fighters in Gao. They are Nigerians and from Niger," Abu Sidibe, a regional deputy, told AFP. "They're not hiding. Some are even able to speak in the local tongue, explaining that they are Boko Haram."
Boko Haram militants "were in a majority among those who attacked the Algerian consulate" in Gao, another Malian security official said.
Responsibility for the attack on the Algerian embassy and the kidnapping of diplomats was claimed in a statement issued by an Al-Qaida dissident group, the Movement for Unity and Jihad in West Africa (Mujao).
Mujao is said to have split from the main al-Qaida group in the region, Al-Qaida in the Islamic Maghreb, in order to focus on spreading jihad in West Africa.
Mali has been rocked by political instability after the government was overthrown by a military coup.
The junta said it was forced to act after the government was unable to stop the Tuareg-backed rebellion in the north.
Since taking charge, however, the junta has been unable to stop the Tuaregs, who have now been joined by other Islamist groups.
Coup leader Army Captain Amadou Sanogo met with the country's parliamentary speaker, Dioncounda Traoré, to discuss a transition back to constitutional rule.
Traoré is set to be sworn in as interim president to oversee a transitional period and to organise elections.
Mali's previous president, Amadou Toumani Touré, resigned last week, following a deal with the junta that called for an interim president and the lifting of sanctions imposed by the Economic Community of West African States.