Mobile solar-powered streetlamps made from old bicycle parts are transforming lives in Mali, where villagers often work by night to escape the heat despite 90 per cent having no mains electricity.

The project is the brainchild of Italian architect Matteo Ferroni, who visited the Segou region, 235 kilometers (150 miles) northeast of Bamako, in 2010 and noticed the locals were mainly sleeping during the searing day and getting up in the evening to work.

Tuareg rebels have made further advances in northern Mali and have seized two towns, Kidal and Menaka, the United Nations confirmed on Thursday.

U.N. spokesman Stephane Dujarric told reporters that fighters from the National Movement for the Liberation of Azawad (MNLA) had taken the towns after clashes with Malian government forces.

Mali was in crisis Thursday after its troops were driven out of the flashpoint town of Kidal by Tuareg separatists in a humiliating defeat forcing the government to call for an "immediate ceasefire".

Ministers have not revealed how many lives have been lost in clashes with the National Movement for the Liberation of Azawad (MNLA) and other armed groups in Kidal since fighting broke out on Saturday.

Tuareg militants fighting the Malian army in the rebel stronghold of Kidal said Wednesday they had taken control of the flashpoint town, taking prisoners.

"We now control the whole town of Kidal, we have prisoners," Mohamed Ag Rhissa, one of the leaders of the National Movement for the Liberation of Azawad, told Agence France Presse by telephone.

Mali's army exchanged fire with Tuareg militants in the rebel stronghold of Kidal on Wednesday, witnesses told AFP, shattering an uneasy calm which had held since deadly weekend clashes between the two sides.

The fighting comes after the National Movement for the Liberation of Azawad (MNLA) took 32 civil servants hostage at the regional governor's offices on Saturday, during a battle which left eight Malian soldiers and 28 rebels dead.

The U.N. Security Council called Tuesday for an immediate end to violence in northern Mali after more than 30 people were killed in fighting between rebels and the army in a flashpoint town.

Tuareg separatists clashed with Malian soldiers in Kidal during a visit by Prime Minister Moussa Mara, whose government is backed by French soldiers who have helped dislodge rebels and armed Islamic extremists from northern towns. 

France has delayed plans to pull troops out of its former colony Mali after a fresh bout of clashes in a key town.

France said earlier this month it was ending its "frontal war phase" in Mali after sending troops there in 2013 to free the country's vast desert north from Islamists and Tuareg rebels who seized control after a coup.

President Ibrahim Boubacar Keita warned Monday that "odious crimes" that have left more than 30 people dead in northern Mali would not go unpunished even as Tuareg rebels released civil servants taken hostage in a deadly siege at government offices there.

Around 30 hostages kidnapped by Tuareg rebels in a deadly siege at local government offices in northern Mali were released on Monday, the United Nations said.

"We have just taken back around 30 hostages. They are in not bad condition. Two are very tired," an official from MINUSMA, the United Nations peacekeeping force in Mali, told Agence France Presse.

Mali sent troops on Monday to retake the rebel stronghold of Kidal after Tuareg separatists seized local government offices, taking hostages and engaging the army in a firefight in which dozens were killed.

Eight soldiers and 28 insurgents died in fighting Saturday outside the regional governor's offices while around 30 civil servants were being held hostage by the militants, the government said.