Mali has sworn in an interim president tasked with organizing new elections and fighting Tuareg rebels and Islamist militants.

After his swearing in Thursday in the capital, Bamako, President Dioncounda Traore warned the rebels and al-Qaida-linked group Ansar Dine to retreat or face war.

The former parliament speaker added, “We prefer peace, but if war is the only solution, we will wage it.” Mr. Traore warned the new transitional government “will never negotiate the breakup of Mali.”

Mr. Traore's predecessor, Amadou Toumani Toure, was ousted last month by renegade soldiers who objected to his handling of the Tuareg rebellion.

After the coup, rebels and militants launched a rapid offensive and took the north from the Malian army, proclaiming the region an independent state they call “Azawad.” African nations have rejected the rebel proclamation.

On Thursday, the U.N. human rights chief said the world body has reports that civilians in the north have been “killed, robbed, raped and forced to flee.”

Navi Pillay cited reports that various rebel groups have been preying on individuals and looting property, including hospitals and health care facilities.

Mr. Traore will have up to 40 days to organize a new election.