Ethnic Tuareg fighters returning to Mali from Libya are said to have helped to launch a new rebel group.
The National Movement for the Liberation of the Azawad says it is the result of a merger between two rebel groups, boosted by Tuaregs who fought for Col Muammar Gaddafi in Libya.
Mali's Tuaregs have long complained that they have been marginalised by the southern government.
The NMLA wants independence for northern Mali's desert region.
The Tuareg are a nomadic community who mostly live in the Sahara desert and nearby regions of countries across north and west Africa.
Mali has been saying since the start of the conflict in Libya that the fall of Col Gaddafi would have a destabilising effect in the region.
The BBC's Martin Vogl in the capital, Bamako, says this latest development is why Mali was such a strong supporter of the African Union position on Libya, which favoured a negotiated settlement instead of the Nato-led bombing campaign.
Our correspondent says that ethnic Tuaregs with dreams of a new rebellion have decided to seize the moment, with the return of their well armed and well trained brothers, to present a tougher stance.
He says their demands are more radical than those of previous rebel groups.
NMLA spokesman Hama Ag Sid'Ahmed said high-ranking officers from Libya had joined the new group.
"We've overcome our differences and will now present common political demands which reflect the profound aspirations of this population," he said.
The NMLA has demanded that the government opens negotiations before 5 November.
Our correspondent says it not clear whether this group is capable of carrying out large scale military operations or is willing to do so, but that even if it were to launch some small raids on isolated military bases it would be a huge change in the status quo.
Security is already a concern in northern Mali following attacks by al-Qaeda's north African wing.
In a sign of the government's concern, Interior Minister General Kafougouna Kona is heading to the region this week.
Our correspondent says he is one of President Amadou Toumani Toure's most trusted men and someone who has a lot of experience negotiating peace with rebel Tuareg factions.
Before he was ousted, Col Gaddafi had helped broker a deal to end a Tuareg rebellion in neighbouring Niger.
Many former fighters then went to Libya to join the army.
But in recent months, convoys of former Gaddafi loyalists have been crossing the desert to escape reprisals by the forces who ousted Libya's long-time leader.