Niger on Monday declared three days of mourning and vowed to beef up security in a western border region where jihadists killed 100 villagers, according to a local toll.

"We have decreed three days of national mourning, and on security, we are going to strengthen the presence" in the frontier region with Mali, Interior Minister Alkache Alhada told AFP, adding that the government would also launch "forums" to defuse ethnic tension.

Scores of "terrorists," arriving by motorbike, killed 70 people in the village of Tchoma Bangou and 30 in Zaroumadareye, local mayor Almou Hassane told AFP on Sunday.

It was the biggest single massacre of civilians in the Sahel's eight-year-old history of Islamist unrest, according to a US group, ACLED, which tracks the violence.

Alhada, speaking by phone after a meeting of the National Security Council headed by President Mahamadou Issoufou, said troop numbers would be increased to achieve "greater saturation" of the area.

"We have to stop incursions. We have to create a kind of security cordon, but one of the difficulties is that there's a void on the Malian side," he said.

Alhada also promised support, in the form of food aid, for communities who had suffered losses.

Niger is caught in a pincer between jihadists crossing from Mali, in its southwest, and from Nigeria, in its southeast.

Thirty-four people were killed in the southeastern region of Diffa on December 12 by Boko Haram jihadists.

Map of Niger locating the Tondikiwindi district where two villages were attacked by gunmen
Map of Niger locating the Tondikiwindi district where two villages were attacked by gunmen AFP / Kun TIAN

Its armed forces, poorly equipped and trained, have lost nearly 200 men to road bombs and camp raids in the last two years.

The government has previously unveiled plans to double military personnel to "at least 50,000" over the next five years. Defence already accounts for 17 percent of the budget.

The jihadist insurgency in the vast Sahel began in northern Mali eight years ago, and then spread into Niger and Burkina Faso.

Thousands of people in those countries have died and nearly three million people have fled their homes, according to UN figures.

Jihadist violence has also fuelled ethnic tensions.

Alhada said the government would stage forums with ethnic and religious leaders to "prevent the risk of intra-ethnic conflict" in the border area.

"In this region which is a string of multi-ethnic villages, these incursions can lead to intra-community conflict. We have to make people aware of this," he said.

"I was there yesterday with the prime minister. It's hard -- we saw the graves, the victims' relatives. We have to hold back (anger) to prevent flareups. Some people are calling for weapons," Alhada said.