Army chiefs from four Sahel nations met in Nouakchott on Wednesday to discuss the worsening security crisis in occupied northern Mali, the Mauritanian press agency reported.

"Army chiefs from Mauritania, Algeria, Mali and Niger are looking into the evolution of the security situation in northern Mali" in a closed door meeting, the press agency AMI reported.

They have "examined the means to assist the Republic of Mali to recover its sovereignty in all its national territory."

Once one of west Africa's most stable democracies, Mali plunged into crisis earlier this year when a coup d'etat opened the way for armed groups to seize the vast north, an area larger than France.

Initially spearheaded by Tuareg rebels, the nomadic desert tribesmen have been pushed aside as Islamist fighters linked to Al-Qaeda in the Islamic Maghreb took the upper hand, and now control key northern cities.

The hardline Islamists have enforced sharia and destroyed ancient cultural treasures which they consider idolatrous, despite a chorus of international condemnation.

An interim government which took over from the junta has proved powerless in the face of the armed groups, and has been ordered by West African mediators to form a more inclusive unity government by July 31.

The army chiefs also discussed measures to support a joint military operations committee to which all four countries belong.