Nigeria’s new president, Muhammadu Buhari, dismissed all of his country’s top military officials on Monday, his spokesman announced, after weeks of mounting violence in which Boko Haram fighters have killed hundreds of civilians, The New York Times reported.

The Nigerian military’s handling of Boko Haram’s bloody six-year uprising has been widely seen as dismal. It has been faulted not only for failing to stem the extremist group’s murderous rampages, but also for making the situation worse through widespread human rights violations.

The country’s news media has been urging Buhari for weeks to get rid of the architects of what is seen in Nigeria as a failed campaign to stop the Islamist militant group. On Monday, some analysts questioned why Buhari, who took office in late May, waited so long.

“The surprise for me is that it didn’t happen much earlier, given the terrible performance of the armed forces,” said Jibrin Ibrahim, a political scientist. “We thought it would be one of his first acts.”

Two of the officials who were dismissed on Monday — Alex Badeh, the chief of the defense staff, and Lt. Gen. Kenneth Minimah, the head of the army — were cited in a recent Amnesty International report, which accused them of being responsible for war crimes committed under their command.

Buhari, a former general who once ruled the country as a military dictator, also replaced his national security adviser, Sambo Dasuki, on Monday. As the coordinator of Nigeria’s strategy against Boko Haram, Dasuki has been the object of particularly sharp criticism.

The purge comes a week before Buhari is scheduled to visit Washington, meet with President Obama and work on strategy against Boko Haram with American officials. Relations between the American and Nigerian militaries were all but frozen under Buhari’s predecessor, Goodluck Jonathan, with the American side denying assistance on a broad range of issues to a military that was broadly tainted by well-documented human rights violations.

“This is a really big meeting, where they are going to try to be in sync with the Americans,” Paul Lubeck, a Nigeria specialist at Johns Hopkins, said of the trip to Washington. “They want help from the Americans.”

Buhari immediately announced replacements for the fired officials. Most significant is the elevation of Maj. Gen. Tukur Yusuf Buratai, currently the head of the multinational anti-Boko Haram force based in Ndjamena, Chad, to be the new army chief of staff. Coordination among armies in the affected region — those of Cameroon, Chad, Niger and Nigeria — has been notoriously poor, and the other three countries say Nigeria has been at fault.

Now, with General Buratai, Buhari is “focusing on somebody who has skills with the different armies,” Lubeck said. Underscoring the regional threat, over last weekend Boko Haram staged attacks here in Niger, where militants struck a prison in Diffa, east of the capital, Niamey; a suicide attacker, a man in a full-face veil disguised as a woman, struck a market in Ndjamena, killing at least 15 people; and a suicide attack in northern Cameroon killed about a dozen civilians.