Former rebels in Mali held a failed reconciliation forum in their northern bastion of Kidal which was boycotted by the government, as the UN warned of an "alarming" security situation.

Pro-Bamako armed groups also shunned this week's meeting after the Coordination of Movements of the Azawad (CMA) ex-rebels allegedly refused the government's conditions that troops should be allowed into the city and the national flag be flown.

"We aren't going to go to Kidal as if it is another country, that's not possible," a government minister told AFP.

The government has not had any presence in Kidal for several years and the army was driven out in 2014.

The forum brought together those sympathetic to the primarily Tuareg rebels' cause from as far as Mauritania, with discussions centred on establishing a better climate for future talks and calls for greater freedom of movement in the surrounding area.

"We want to create a climate of understanding between the communities, which is indispensable for implementing the peace deal," CMA leader Alghabass Ag Intalla said in a speech.

Although a landmark peace agreement was reached last year between the government and the rebels, the CMA has since violently clashed with pro-government armed groups, the so-called "Platform."

Subsequent "pacts of honour" have toned down their fighting but Mali is wracked by a raging jihadist insurgency that has widened despite Islamists being routed from northern towns in 2013.

On Tuesday, two Malian soldiers were killed and two others injured when the vehicle they were travelling in was blown up by an explosive device in the Timbuktu region, to the west of Kidal.

UN Secretary-General Ban Ki-moon said Monday he was "concerned that actual progress in the implementation of the peace agreement remains limited."

Aside from dealing with the ex-rebels, he said, "the northern and central parts of Mali remain under the threat of criminal, violent extremist and terrorist groups, which take advantage of the limited presence of Malian law enforcement institutions."

Mali's vast, desolate north fell under the control of the Tuareg-led rebels who allied with jihadist groups linked to Al-Qaeda in 2012.

The Islamists were largely ousted by an ongoing French-led military operation launched in January 2013, although they have since launched sporadic attacks on security forces from desert hideouts.

However, rival armed factions and smuggling networks mean the region has struggled for stability since the west African nation gained independence in 1960.