Mass killings by armed herdsmen, amid clashes with farming communities in the central-belt region of Nigeria, have claimed the lives of hundreds of people. The government had increased security in affected states, but the military spokesman, Gen. John Agim, admitted last month that there was no military presence in Benue, the state most affected by the clashes.

Chidi Odinkalu, a human rights activist in Abuja, said there had been a significant collapse of security in Nigeria.

“The government’s response in these killings in Kaduna, as in Benue, as in all these affected regions, has been to deploy soldiers,” he said. “But the military is stretched already so it is making other security challenges worse.” Moreover, officials are not trying to understand or resolve “the root causes of the problems,” he added.

Mr. Odinkalu said that the killings by bandits could only happen because of government failings. “Banditry occurs in ungoverned territory,” he said. “It’s in these rural areas with little or no cover. The territory is completely exposed, so at the heart of the issue is a crisis of governance.”

Mr. Buhari came to power promising to end the Boko Haram insurgency, which has left more than 20,000 dead, and millions displaced and in need of humanitarian aid. He and the military have repeatedly claimed to have defeated the terrorist group, but it has stepped up its attacks this year, killing hundreds of people at mosques, markets and other gathering places.

Last week, at least 27 people were killed when a suicide bombing ripped through a mosque and market area in Adamawa State. In February, Boko Haram militants kidnapped 110 schoolgirls from Dapchi Town, though they returned 104 of the girls less than a month later; five other girls died, and they continued to hold one, Leah Sheribu, a Christian who refused to convert to Islam.

On Monday afternoon, the Nigerian Army said that it had rescued more than 1,000 people, mostly women and children, who had been held captive by Boko Haram militants in the Bama area of Borno State. The military has in the past announced numerous rescues of people kidnapped by Boko Haram, but it generally offers few details about the operations and provides limited access to journalists seeking to independently verify the claims.

According to Amnesty International, thousands of men women and children have been abducted by Boko Haram during its insurgency.