Unidentified armed men massacred 31 civilians in simultaneous attacks on several Mali villages this week, then killed nine soldiers responding to the assault as violence surges in the country's conflict-wracked centre.

An Islamist insurgency that erupted in the north of the vast West African country in 2012 has swept to its centre, inflaming ethnic tensions along the way. 

Clashes between the ethnic communities of Fulani, nomadic herders, and Dogon traditional hunters have increased in recent months, with community-based militias -- initially formed for defence -- now launching attacks.

Armed uniformed men travelling in pick-up trucks attacked four Dogon villages on Wednesday, one local official said by telephone, speaking on condition of anonymity for security reasons.

The attack left at least 30 dead, including women, children, and the elderly, while others were missing, the official added. 

"From 3 to 9 pm, nobody came to our rescue," said Youssouf Tiessogue, an elder from Gouari, one of the villages attacked.

Deploring the army's "inaction," he said: "It is always late and never confronts the bandits even if we tell them where they are." 

A senior government official called the attacks "barbaric". 

Officials did not immediately blame any group.  

A military unit was dispatched to the area, and helped bury 31 bodies on Wednesday, army spokesman Colonel Diarran Kone told AFP.

On Thursday, the army received information about a new attack and sent the unit to Gouari, he said.

"When it arrived at around 8 pm, the village seemed deserted, there were practically no signs of life," he said. 

"Just at the entrance, the FAMa (Malian Armed Forces) walked into an ambush," he said, adding that nine soldiers were killed and two wounded.

The attacks were not far from the village of Ogossagou, where 31 civilians were killed in February and 160 were butchered last year -- all Fulani.

Tit-for-tat killing 

Unrest in central Mali has killed nearly 600 civilians this year, the United Nations said last month.

Mali's war erupted in 2012 when Tuareg rebels supported by armed Islamists took over the country's desert north.

The rebels were then outmanoeuvred by their Islamist allies and the French military intervened to force them back.

The conflict has since travelled south, as well as spilling into neighbouring Burkina Faso and Niger, igniting a tinderbox of ethnic resentment and stoking fears for the future of the fragile nation. 

Armed groups coming from the north found fertile soil in an area riven by long-running land disputes, often between herders and farmers.

Central Mali is now prey to tit-for-tat killings and routine jihadist attacks. Hundreds of thousands of people have been displaced.

A jihadist group active in the region led by radical Fulani preacher Amadou Koufa has also increased suspicion of his ethnic group.

In response to jihadists, traditional Dogon hunters have formed so-called self-defence groups, adding to the tension.

More than 5,000 French troops, a regional G5 Sahel military cooperation deal and a UN peacekeeper mission in Mali have not been enough to contain the violence.