Nigerian police said Friday that officers had arrested seven suspects in connection with the massacre of dozens of villagers in central Plateau state.

State police spokesperson Alfred Alabo said security operatives had restored calm to the affected Kubwat and Fungzai villages in the remote Mangu district. He said police would continue to monitor the area to try to prevent more attacks.

Witnesses said gunmen invaded Mangu early Tuesday morning and opened fire on villagers. They also burned many houses before security forces arrived.

Residents said more than 100 people were killed, and they blamed ethnic Fulani militias for the bloodshed.

Alabo said that even before the attacks, tensions had been high in the area because of disputes between farmers and herders over grazing land.

In a phone interview with VOA, he said he was not sure of the death toll.

"It's a place that was riddled with crisis," he said. "You can't just be jumping [to conclusions] and be giving figures. They told me over 30 persons at that time, so we'll get more information."

Residents said thousands of people who fled their homes to escape the violence had yet to return to the villages.

But Alabo said the situation had been brought under control. "We have so far been able to calm the situation in that general area," he said. "But we're still monitoring. We have some suspects already in custody presently with Operation Safe Haven."

Communal clashes over scarce grazing land and water resources have plagued Nigeria's central region for decades. Benue, Nasarawa and Plateau states are among the ones most impacted by the disputes.

On Thursday, rights group Amnesty International condemned the killings and called for accountability. Police have promised to continue investigating.

A Plateau state resident, who survived the attack and asked for safety reasons that his name not be used, said security officials arrived too late.

"It was something that I never expected to happen," he said. "Many people were killed. It was a big tragedy, what I saw in that place. About 100 people were killed, many were displaced, and some are in the hospital."

Nigerian authorities are struggling to control a wave of violence across the country.

On Tuesday, police announced they were investigating an attack last week in which gunmen killed 15 people in a farming community in Nasarawa state. Police said those killings appeared to be carried out in retaliation for the death of an ethnic Fulani herder who was attacked days earlier. (Text, excludes headline: VOA)

•Clashes over grazing land and water have plagued central Nigeria for decades. Victims of farmer-herder clashes recovered in this ward at Jos University Teaching Hospital in Jos

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