Deadly clashes have broken out in northern Mali between the army and rebels, who seized 28 people as the prime minister visited the area.
At least 36 people reportedly died in Kidal as Tuareg rebels fought troops on Saturday before and during PM Moussa Mara's visit.
When he left the governor's office in Kidal, the building was seized by the rebels, an eyewitness told the BBC.
In 2012 a Tuareg rebellion in northern Mali triggered a military coup.
Civilian rule was re-established in 2013, but Islamist and separatist forces remain active in some areas.
"Eight members of the armed forces were killed and 25 were wounded, while 28 of the attackers were killed," the defence ministry said.
Mr Mara said that the government was now "at war" with the separatists. President Ibrahim Boubakar Keita is expected to give a national address on Monday.
Malian Defence Minister Soumeylou Boubeye Maiga said on Sunday that reinforcements would be sent to Kidal.
"We will double our troops on the ground if necessary," AFP news agency quoted him as saying.
Mr Mara spent Saturday night at the Malian army camp in Kidal, flying to Gao early on Sunday morning.