President Muhammadu Buhari vowed on Tuesday there would be no mercy for those behind the killings of more than 100 people in a series of attacks in central Nigeria.

Gunmen raided and ransacked a group of villages there, local sources said, in one of worst attacks this year blamed on heavily armed criminal gangs.

Condemning what he called the heinous killings, Buhari promised that the perpetrators would receive "no mercy."

"They should not be spared or forgiven," he said in a statement.

Sunday's attacks in Plateau State and a high-profile kidnapping raid on a train in neighboring Kaduna State have highlighted intensifying insecurity in northwest and central regions of Africa's most populous nation.

On Sunday, gunmen attacked more than four villages in Plateau, leaving more than 100 people dead with scores of homes destroyed, two local community leaders and the commander of a local vigilante force said Tuesday.

Details of the attack were still sketchy, with local officials and security forces confirming the assault but declining to give a death toll.

"Many people were killed with houses and properties destroyed," Plateau State Governor Simon Bako Lalong said in a statement that condemned the violence but gave no precise toll.

One local community leader, Malam Usman Abdul, told AFP on Monday that 54 bodies were found at Kukawa village, 16 local vigilantes were also found dead at Shuwaka village, 30 villagers were recovered at Gyambahu and four more were found around other villages.

"People are still looking for their family members," he said.

Bala Yahaya, operational commander of the local vigilantes who work with security forces told AFP they had recovered 107 bodies, including 16 members of his group.

Another community leader gave a similar figure for the number of fatalities.

Residents said there were mass burial services on Monday for the victims of the attack in four adjoining villages.

Security forces and local government officials did not respond to requests for confirmation of a toll.

Major Ishaku Takwa, military spokesman, said on Monday that many villages had been ransacked but that the number of casualties was still being verified.

Northwest and central states in Nigeria have long struggled with a security crisis that has emerged from tensions and clashes between farmers and herders over water and land.

Tit-for-tat revenge killings spiraled into broader criminality as gangs known locally as bandits with hundreds of members targeting villages for raids, mass kidnapping and looting.

Despite a military campaign to flush them out of their forest hideouts, attacks by bandit gangs have intensified.

Last month, gunmen blew up rail tracks and attacked a train between the capital Abuja and the northwestern city of Kaduna, killing eight people and abducting an unspecified number of other passengers.

They later released videos showing their hostages.

The train attack came two days after bandits killed a security guard at the perimeter fence of Kaduna's airport, prompting two local airlines to temporarily halt flights into the city.

Nigeria's overstretched security forces are already battling a grinding 12-year jihadi insurgency in the country's northeast, where Boko Haram and Islamic State West Africa Province are operating.

The conflict has killed more than 40,000 people and forced around 2.2 million more people to flee their homes since it erupted in Borno State in 2009.