Tuareg rebels have been in conflict with the government since independence
Suicide bombers and armed attackers have killed about a dozen people in an assault on rebel positions in northern Mali, security sources have said.
This is the first suicide bombing blamed on the pro-government Gatia militia fighting Tuareg rebels.
However, it may have been infiltrated by militant Islamists who joined the attack, correspondents say.
Northern Mali has been hit by conflict between government forces, Tuareg separatists and militant Islamists.
French-led troops beat back al-Qaeda-linked groups who had seized control of most of the region in 2012 with the backing of the National Movement for the Liberation of Azawad (MNLA), the main rebel group campaigning for the rights of ethnic Tuaregs.
'Very volatile'
The MNLA and the al-Qaeda-linked groups later fell-out, and animosity between them now runs strong, correspondents say.
The UN has a 9,000-strong force trying to restore stability in Mali.
The UN is battling to end the conflict
Correspondents say there are strong suspicions that the government is increasingly relying on militia groups such as Gatia to strengthen its position against the MNLA in the north.
A UN source told the AFP news agency that two bombers blew themselves up in the attack near Tabankort town while a third was killed before he could detonate himself.
"Gatia fighters, accompanied by suicide bombers, attacked a rebel Tuareg and anti-government Arab position in the night from Tuesday to Wednesday near the town of Tabankort. There were a dozen deaths in total," a Western military source told AFP.
"The situation is very volatile, and it is essential to calm the situation," added the source.
The BBC's Alex Duval Smith in the capital, Bamako, says details around the attack are still unclear.
However, only al-Qaeda-linked groups have up to now carried out suicide bombings in Mali, and it is likely that they have infiltrated Gatia.
On Tuesday, three people were killed during clashes between protesters and UN troops in Tabankort, a stronghold of Gatia.
The protested stormed the UN base in Tabankort, accusing it of planning to create a buffer zone that would favour the MNLA. The UN denied there was such a plan.
Last week, the UN launched air strikes to push back MNLA fighters who had launched an assault to capture Tabankort from Gatia, the French acronym for Imghad and Allies Tuareg Self-Defence Group.
Northern Mali has been a flashpoint of conflict since Mali's independence from French rule in 1960, with Tuareg rebels campaigning for independence or more autonomy.
The conflict has become more complex with emergence of jihadi groups, which roam freely across large parts of the Sahara desert.