Mali's new interim president, who took over from coup leaders Thursday, is threatening "total war" against the Tuareg and Islamist rebels who have seized half the country since the putsch three weeks ago.
Former parliament speaker Dioncounda Traore took the oath of office in the west African nation at a ceremony Thursday attended by, among others, junta leader Captain Amadou Sanogo, who initially grabbed power in the March 22 coup.
Mali's new interim leader - a 70-year-old mathematician turned politician who speaks six languages - is expected to soon name a prime minister, and to organise elections within 40 days.
The mutineers justified last month's coup by accusing the former government of mishandling the Tuareg rebellion - but their action allowed the Tuareg and Islamist militants to take over a vast area in the desert north, effectively splitting the country.
Amid the disarray in the capital, they captured an area the size of France, including the ancient town of Timbuktu, bringing lawlessness to an area already gripped by drought and acute food shortages.
Traore said he was "aware of being the president of a country at war" and warned that the rebels must "stop the... pillaging, the rapes. They must leave the cities that they have occupied."
If they did not, he said, "we will not hesitate to wage a total and relentless war."
The Group of Eight rich nations voiced "deep concern for the deteriorating situation in northern Mali and the implications the current crisis has for the wider Sahel region, including the impending humanitarian crisis."
The G8 foreign ministers, meeting in Washington, said they had "reinforced their support for the territorial integrity of Mali... and urged all parties to ceasefire and engage in political talks."
A US State Department spokeswoman said the United States welcomed Traore's inauguration as a positive step in the country's political transition process, urging "all parties to facilitate the swift and complete restoration of civilian rule through free and fair elections."
The African Union also applauded the handover of power to Traore.
The State Department however expressed deep concern at reports of human rights violations in the north.
Meanwhile ECOWAS foreign ministers met in Abidjan Thursday to consider sending a regional force into northern Mali.
The rebellion there "constitutes a real obstacle to the peace process," said Ivorian Foreign Minister Daniel Kablan Duncan after the meeting of the 15-nation Economic Community of West African States (ECOWAS), which mediated the Mali power transfer.
On the possibility of sending in a force, Duncan said "the resolutions will be handed over to the ECOWAS heads of state," as fears rose that the rebel-held region could become a haven for radical Islamists.
The coup leaders, Malian politicians and ECOWAS mediators are scheduled to meet in Burkina Faso this weekend to clarify the still murky management of the transitional period.
In Mali, five ministers and four other politicians of ousted president Amadou Toumani Toure's government were released Thursday, according to Captain Moussa Dindo, who is close to the junta, and family members.
The nine had been held at the coup leaders' headquarters, a military camp at Kati, near the capital Bamako.
The junta is expected to retain some influence, with observers saying coup loyalists could be named to key ministerial posts, notably those linked to security as the army tries to reverse the massive rebel gains.
Many of the Tuareg rebels, who have fought several separatist campaigns over the years, are heavily armed and battle-hardened from last year's Libya war where they fought as mercenaries for slain dictator Moamer Kadhafi.
Joined by Islamist extremists linked to Al-Qaeda in the Islamic Maghreb (AQIM), they made unprecedented gains in the weeks since the coup.
The main Tuareg rebel group, Azawad National Liberation Movement (MNLA), has declared an independent state, a call rejected by the international community and by the MNLA's former Islamist allies.
Ansar Dine, the Islamist group that controls several key towns, has imposed sharia law in some areas under its influence and distanced itself from the Tuareg nationalist cause.
The UN Security Council has warned of the growing "terrorist threat" in northern Mali, while the world body's rights chief Navi Pillay said violations could be worsening in the rebel-held north.
Reports "suggest that civilians have been killed, robbed, raped and forced to flee", she said in a statement.
Both Ansar Dine and AQIM are recruiting children in a bid to boost their forces, a local elected official and a journalist in the region told AFP.
Ansar Dine, backed by AQIM, meanwhile took control of Timbuktu's renowned centre of historic manuscripts which keeps between 60,000 and 100,000 documents, sources said.