Islamic extremist in Mali's north have killed at least 15 people in two attacks in the Kidal region near the border with Algeria, a jihadi group and resident said.

Militants with the Ansar Dine extremist group killed 11 people in an attack on Tuareg rebels near the Algerian border in Kidal, the militants said in a statement on a jihadi website Saturday.

"The attack resulted in the release of mujahedeen prisoners and the recovery of vehicles and weapons," it said.

Four people were killed Friday during an ambush by Ansar Dine on a Tuareg separatist vehicle, including the younger brother of the secretary-general of the separatist group that signed a peace deal with the government in late June, said a Kidal resident who spoke on condition of anonymity to protect his security.

Ansar Dine and other extremist groups, including al-Qaida's North Africa branch with which it is allied, have spoken out against the peace accord, accusing separatists who signed it of betraying the local population.

The attacks on Tuareg separatists were likely in retaliation for the killing of Ansar Dine militants by the separatists on December 19, said a Tuareg separatist who spoke on condition of anonymity because he did not have permission to speak to the press.

An anti-extremist unit of the separatists killed at least four jihadis and imprisoned four others, the separatist said.

Islamic extremists took hold of Mali's north after a power vacuum in the south in 2012. A French-led operation ousted the jihadis in 2013, but attacks and unrest continue, moving further south.