Mali's prime minister, Moussa Mara, has said his country is now "at war" with Tuareg separatists , following a battle between government forces and members of the nomadic rebel group that killed at least 36 people, the defence ministry said.

Mara made the statement on Sunday after clashes between the two sides in the northern city of Kidal on Saturday also caused at least 30 people to be taken hostage, according to government officials.

"In light of this declaration of war, the Republic of Mali is henceforth at war," Mara told the Reuters news agency. "We are going to formulate the appropriate response to the situation," he said.

The fighting started on Saturday outside the regional governor's offices as Mali's prime minister visited the city of Kidal as part of his first tour of the country's restive northern desert.

RELATED: The fight for a Tuareg homeland

"During the fighting, eight members of the armed forces were killed and 25 were wounded while 28 of the attackers were killed," the defence ministry said in a statement.

A source from the governor's office told the AFP news agency that about 30 of the office's personnel were reported missing.

"We do not know their fate. We also do not know exactly how many of them are being held by the rebels," the official said.

Tuareg takeover

A spokesman for the MNLA, a secular separatist Tuareg rebel group that wants an independent state in northern Mali called Azawad , claimed control of the town of Kidal on Sunday.

"We've taken about 40 prisoners, including high-ranking military officers and civil servants," said Attaye Ag Mohamed, a MNLA spokesman. "They're all safe and sound and doing well," he told Reuters.

He added that Mali's United Nations peacekeeping mission had called for a ceasefire and that there had been no fighting on Sunday.

"The town is completely secured by us...the army are back inside their base. If they attack us, however, we'll fight back," Mohamed said.

Mali, a former French colony, was thrown into turmoil in 2012 when al-Qaeda-linked fighters took advantage of a Tuareg-led rebellion and seized control of the country's north.

A French-led military operation drove back the fighters last year, but the Mali government has shifted its focus to the Tuareg rebels.

Mara criticised both the French and UN forces in the country for allowing the attack to take place on Saturday.

"You were witnesses today to the more than passiveness of these forces," he said.

For more on the Tuareg struggle for an independent homeland, watch Al Jazeera's three-part documentary series: Orphans of the Sahara.