A confidential UN report says deadly fighting in South Sudan in July was directed by the highest levels of government, and that leaders are intent on a military solution that has escalated the conflict from a “primarily political to tribal war”.

The UN report obtained by the Associated Press says President Salva Kiir and Paul Malong, chief of staff for the Sudan People’s Liberation Army, orchestrated fighting in Juba, the capital, that killed hundreds. MI-24 helicopters that only they had the authority to deploy were used, said the study, which cites “numerous reports” from South Sudanese senior military personnel and politicians.

The report also said Kiir and Malong have focused on procuring new weapons and ammunition, apparently including two fighter jets. Two truckloads of ammunition were transferred from neighbouring Uganda in June. There has been no sign of significant arms procurement by the opposition in recent months, the report said.

South Sudan’s civilians are “bearing the brunt of the resulting harm” as weapons continue to be procured, the report added. “By the government’s own account, the vast majority of government revenue … has funded security expenses and the war effort, including the procurement of weapons, rather than social services.”

The UN security council has threatened to impose an arms embargo if South Sudan’s government doesn’t comply with a plan to deploy an extra 4,000 peacekeepers to protect civilians.

“The findings of the South Sudan panel of experts show the absurdity of waiting even one more day to impose an arms embargo on South Sudan,” said Louis Charbonneau, UN director at Human Rights Watch.

The report also said officials have focused on “mobilising their respective tribes”, which has worsened ethnic tensions. South Sudan’s civil war began in December 2013 between supporters of Kiir, an ethnic Dinka, and his former vice-president Riek Machar, an ethnic Nuer.

Tens of thousands of Nuer have taken shelter in UN camps in South Sudan under often dire conditions as a peace deal, signed a year ago, threatens to fall by the wayside amid continued fighting. During the July violence, “house-to-house searches were conducted in at least five neighbourhoods in Juba, targeting mainly Nuer men and women, but also individuals perceived as ‘anti-government’,” said the report.

The government and rebels’ “arming of communities based on tribal affiliation continues to fuel widespread violence”, it added.

The report comes just days after a security council visit to South Sudan designed to put pressure on the government to allow in the 4,000 additional peacekeepers. A joint statement by the council and the government said South Sudan accepted their deployment but, just after the diplomats left, government officials announced conditions. These included prior approval of troop contributors and the weapons carried by them.

The visiting diplomats also pressed South Sudan’s government to hold accountable soldiers accused of rampaging through a hotel compound popular with foreigners in the July chaos.

The report said 80-100 soldiers overran the Terrain compound and “raped and gang-raped at least five international aid workers and an unknown number of staff working at the compound, and executed John Gatluak, a Nuer employee of the NGO Internews in front of his colleagues, in an ethnically targeted killing”.

The report added: “This attack was well coordinated and cannot be considered as an opportunistic act of violence and robbery.”