The UN has voiced concerns over Mali's shaky peace deal following deadly clashes between groups that have signed up to the agreement.

The clashes last week -- between pro-government group GATIA (the Imghad and Allies Tuareg Self-Defence Group) and ex-rebels from the Coordination of Azawad Movements (CMA) -- left around a dozen fighters dead near the flashpoint northeastern town of Kidal.

"These clashes, as well as constituting repeated violations of ceasefire accords, threaten the progress achieved up until now in the implementation of the peace agreement," the UN's mission in Mali, known by the acronym MINUSMA, said in a statement on Wednesday.

The mission expressed "serious concern over the deterioration of the security situation and over reported allegations of human rights violations" and complained the unrest was hampering the delivery of humanitarian aid.

The UN called on parties involved in the peace deal to "take immediate measures to guarantee the protection of civilians and refrain from all action that could unleash a return to hostilities".

The Algeria-led international mediation team, which includes the UN, EU, African Union and the regional bloc ECOWAS, also said it was "deeply concerned" by the clashes and threatened sanctions targeting those responsible.

It "believes that this situation cannot continue longer without compromising the essence of this agreement" concluded in May-June 2015, according to a statement issued after a meeting of the committee monitoring the peace deal.

The mediation group threatened "sanctions by the international community" against those found responsible "individually or collectively" for the persistent deadlock.

It urged all parties to "fully respect their commitments and their responsibilities and demands, in particular, the government take all necessary measures for a speedy implementation of the agreement".

GATIA said this week that it had pushed the CMA out of two key villages in the region -- Inekabawatane, and In Khalil, a strategic frontier settlement that sees the transit of all imports from Algeria to northern Mali.

Northern Mali fell into the hands of jihadists linked to Al-Qaeda in early 2012.

Ongoing international military intervention since January 2013 has driven Islamist fighters away from the major urban centres they had briefly controlled, but large tracts of Mali are still not controlled by domestic or foreign troops.

Analysts say tribal rivalries have led to a deterioration of the security situation in the north.