South Sudan's army and the armed opposition are both guilty of “extraordinary acts of cruelty that amount to war crimes,” Human Rights Watch charged last week.

“Thousands of civilians have been killed, homes and markets burned, and bodies left to be eaten by birds and dogs,” the group said in a report based on interviews with over 400 victims and witnesses in South Sudan.

While condemning atrocities carried out by forces allied with rebel leader Riek Machar, HRW accused the military controlled by President Salva Kiir of direct and indirect attacks of a tribal nature.

“Not only are government forces responsible for ethnic-based killings,” HRW said in its 92-page report, “but by failing to take action on many fronts South Sudan’s government has effectively condoned attacks on Nuer civilians and on UN bases.”

“The government has failed to admit the scale of the crimes committed or demonstrate political will to provide accountability,” the rights group added. “Instead President Salva Kiir and other authorities set up a confusing array of investigations, none of which have yielded a public report, hearing or prosecutions.”

Human Rights Watch denounced the government's actions in the same week that President Kiir was cordially received in Washington by US officials.

In a joint appearance with the South Sudan leader on the sidelines of the US-Africa summit, Secretary of State John Kerry offered no criticisms of government actions during the eight-month civil war. Instead, Mr Kerry blamed Mr Machar for breaking a ceasefire agreement.

The US diplomat also reiterated the US view that Mr Kiir is “the duly elected, constitutional president of South Sudan,” while Mr Machar's forces constitute “a rebel group.”

The one-sided criticisms offered by Secretary Kerry elicited dismay from some activists in the US. They also drew a contrast between Mr Kiir's presence in Washington at a time when his homeland is facing famine and the decision by two West African heads of state to skip the summit and remain at home to lead the response to the Ebola emergency.

The United Nations Security Council should “urgently impose an embargo on South Sudan,” Human Rights Watch recommended in its report. It also called for the UN and the African Union to initiate sanctions against individuals responsible for violating international humanitarian and human-rights law.

At the same time, HRW faulted the United Nations for failing to ensure justice for crimes committed during the long civil war that resulted in South Sudan's independence.

In the years following a peace pact in 2005, the international community “focused on increasing the reach of the new Southern government over documenting human rights violations” and punishing those responsible for crimes against civilians. UN missions in South Sudan also did not promote “meaningful inter-communal healing,” HRW said.

The report suggested that the cycle of ethnic violence will continue unless international mechanisms are established to ensure accountability for the slaughters that have occurred during the current civil war.