U.N. Secretary-General Ban Ki-moon on Tuesday fired his top peacekeeping commander in South Sudan, following the release of a damning internal investigation that faulted the top U.N. brass for failing to come to the aid of thousands of civilians.

The U.N. peacekeeping mission in South Sudan fell woefully short of its obligation to protect civilians last summer as fighting between government and rebel forces blew up a fragile peace agreement and pitched Juba into chaos for four bloody July days, according to the scathing inquiry.

United Nations civilian and military commanders were caught unprepared for the fighting, despite multiple warning signs that the capital was headed back into fighting. When the bullets and mortars started flying, U.N. blue helmets abandoned their posts and hunkered down in their compound, leaving thousands of abandoned civilians and international aid workers to fend for themselves.

“The special investigation found that a lack of leadership on the part of key senior mission personnel cuminated in a chaotic and ineffective response to the violence,” according to an executive summary of the report.

Following the report’s release, Ban’s office issued a statement saying the U.N. chief “is deeply distressed by these findings.” His spokesman, Stéphane Dujarric, said the U.N. chief “has asked for the immediate replacement for the force commander,” Lt. Gen. Johnson Mogoa Kimani Ondieki of Kenya. The U.N. chief is considering further action.

Since declaring its independence in the summer of 2011, South Sudan has struggled to form a nation out of a tapestry of diverse ethnic groups. The country has been wracked by violence since December 2013, when forces loyal to President Salva Kiir, a Dinka, opened fire on followers of his former vice president, Riek Machar, a Nuer, setting off a civil war that has had troubling ethnic dimensions.

Earlier this year, an internationally backed peace deal set the stage for Machar, along with more than 1,200 fighters, to return to the capital. But the pact unraveled on July 8, as the capital of Juba erupted into three days violence and chaos as rival forces exchanged fire. The fighting — which left more than 300 dead — marked the total collapse of a fragile peace agreement. It also exposed the vulnerability of U.N. peacekeepers, who came under fierce criticism for abandoning their posts at the height of the fighting and for refusing orders to help humanitarian aid workers.

The U.N. has posted some 1,800 peacekeepers — from China, Ethiopia, India, and Nepal — in Juba. Efforts by the U.N. Security Council to reinforce the troops deployed to the mission, known as UNMISS, have been stalled by the South Sudanese government, which has expressed serious misgivings about the buildup of international forces.

In response to critics, U.N. Secretary-General Ban Ki-moon appointed retired Dutch General Patrick Cammaert to carry out an “independent special investigation” into the U.N. response. The report reveals deep unease about a provision of the peace deal that resulted in Machar and his forces returning to Juba in April to begin the process of forming a power-sharing government in South Sudan.

The U.N. mission’s top official, as well as security experts, raised “strong objections” to deploying Machar’s troops within a kilometer of the U.N. headquarters and two U.N. camps for displaced South Sudanese civilians. They feared doing so would place U.N. personnel and displaced civilians in the crossfire if the rival forces started fighting — but Machar insisted.

The U.N. mission, meanwhile, did not take the warning signs sufficiently seriously.

“Despite the early warning that fighting would take place near U.N. House, the mission did not probably prepare for … foreseeable scenarios,” according to the report’s 10-page summary. For instance, U.N. commanders failed to reinforce defensive positions around U.N. facilities with enough firepower to counter small arms fire, “severely limiting the mission’s ability to respond when fighting with heavy weapons started.”

As fighting intensified, South Sudanese government forces deployed artillery, tanks, and helicopters into the fight.

“Government and opposition forces fired indiscriminately, striking U.N. facilities and POC [Protection of Civilian] sites,” according to the report. “In three days of fighting, two Chinese peacekeepers were killed and several injured, 182 buildings on the U.N. House compound were struck by bullets, mortars and rocket propelled grenades (RPGs).”

The U.N. report reserves some of its sharpest criticism for the peacekeepers who ignored a call for help from 70 civilians, including five U.N. personnel and international aid workers. Some were raped, tortured, and beaten by government troops at Hotel Terrain on July 11. The U.N. Joint Operations Center made multiple requests to peacekeeping contingents, including troops from China and Ethiopia, to send a rapid reaction force to the hotel. Each time, they refused.

Even after the government’s highest-ranking general provided a liaison officer to help the U.N. gain safe passage to the hotel, “no response team materialized.” Three and a half hours after the hotel attack began, South Sudanese security forces extracted all but three survivors. One South Sudanese civilian had already been executed.

One of the three female humanitarian aid workers remaining at the hotel later phoned the U.N. to say they had been left behind. But a U.N. security officer who took the call “was dismissive of her appeal and did not call her back when her phone credit expired,” according to the report summary. In the end, a private security company contracted by an international relief agency rescued the women.

Months after the crisis, U.N. peacekeepers “continue to display a risk averse posture unsuited to protecting civilians from sexual violence and other opportunistic attacks,” the report found.

In one particularly egregious case, U.N. troops and police stood by impassively as attackers assaulted a woman just a few yards in front of a U.N. protection site. “Despite the woman’s screams, they did not react,” the report said. The assault was stopped only after U.N. civilian staff officers “intervened and prevented a further assault.”

The investigators were unable to verify separate allegations that peacekeepers had failed to intervene to stop sexual assaults of women during the July violence in Juba. “While these incidents of sexual violence most certainly occurred, the special investigation was unable to verify the allegations regarding the peacekeepers’ response,” the report stated.

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