GENEVA: U.N. human rights experts called on Monday for an international investigation into horrific abuses committed in South Sudan, reiterating warnings of "ethnic cleansing" in the war-ravaged country.

In a report, the U.N. Commission on Human Rights in South Sudan voiced alarm at the "massive increase in gross human rights violations and abuses" in recent months.

The three commission members warned that the actions of the South Sudanese government and other parties to the conflict suggest "the deliberate targeting of civilian populations on the basis of their ethnic identity by means of killings, abductions, ... rape and the burning of villages."

In the report, to be presented to the U.N. Human Rights Council in Geneva next week, they reiterated their warnings following two visits to the country last year that "ethnic cleansing was under way."

The experts meanwhile called for the U.N. to order "an international, impartial and independent investigation ... into the most serious crimes, including conflict-related sexual violence."

They also urged the African Union (AU) to help ensure the swift establishment of a hybrid court for South Sudan, a key provision of a 2015 peace deal, adding that such a court needed to be operational within six to nine months.

"Unless impunity is addressed and perpetrators of serious violations are brought to account, the viability of South Sudan as a new nation state will be stymied, if it has not been already," the report warned.

South Sudan, the world's youngest nation, was engulfed by civil war in 2013 after President Salva Kiir accused his rival and former deputy Riek Machar of plotting a coup against him.

An August 2015 peace deal was left in tatters when fighting broke out in Juba in July last year.

Violence – initially between ethnic Dinka supporters of Kiir and ethnic Nuer supporters of Machar – has since spread to other parts of the country, engulfing other ethnic groups and grievances.

The conflict has sparked a massive humanitarian crisis, with famine declared in some parts of the country, and millions displaced from their homes.

- Rampant sexual violence -

The U.N. experts said several of the abuses in South Sudan may "amount to war crimes."

Citing reports, the U.N. experts said government soldiers, members of the National Security Service, police officers and pro-government militias appeared to be mainly to blame for the abuses.

However they said opposition fighters had also carried out violations.

Monday's report also raised alarm over the "extremely large number of cases of conflict-related sexual violence," providing excruciating victim accounts of brutal gang rapes.

"Impunity for conflict-related sexual violence has become entrenched, and is a direct consequence of the failure of the government to take action against perpetrators of such violations," it said.