Violence is still raging in vast swathes of South Sudan a year after a peace deal was signed to end a civil war that began in 2013, a United Nations (UN) report said on Friday.

Attacks by armed groups against civilians intensified in 2020 and victims are targeted along ethnic lines, often with the support of government and opposition forces, the report by the UN's Commission on Human Rights in South Sudan said.

The scale of violence exceeds that of 2013 to 2019, commission chairperson Yasmin Sooka said.

Hundreds of people were killed, and hundreds of thousands more displaced during fighting in Central Equatoria, Warrap, Jonglei, and Greater Pibor, the report said.

Women and girls have been "abducted, raped, gang-raped, and sexually enslaved, and in some instances are forcibly married," the commission said in a press release.

Commission member Andrew Clapham said the scale of the violence and the fact that local groups were using newer weapons suggested either the involvement of state forces or external actors.

Acting military spokesperson Santo Domic Chol said it was not the first time the commission had issued such a report.

"We are not against your report, but you need to share it with us so that if there are areas of mistakes that some of our institutions has undertaken, we can change," he said.

However, the government and the army would not accept negative campaigns against institutions waged through the media, he said.

South Sudan won independence from Sudan in 2011 after decades of civil war. Violence erupted in late 2013 after President Salva Kiir, from the Dinka ethnic group, sacked vice president Riek Machar, a Nuer.

The two men have signed many deals to end a war estimated to have killed more than 400 000 people. They repeatedly pushed back deadlines to form a government of national unity, but a year ago finally did so.

In February 2020, Kiir swore in former rebel leader Machar as his vice president. The government later appealed for donor funding to implement the deal, saying it did not have enough money to do so on its own.