Kiev (AFP) - The United Nations on Friday accused both the Ukrainian authorities and pro-Russian rebels of torturing fighters and their sympathisers captured in the separatist east.

The condemnation came with violence once again flaring after a period of relative calm in the 25-month war.

The Office of the UN High Commissioner for Human Rights (OHCHR) said 9,371 people have been killed and 21,532 wounded since the revolt against the pro-Western government in Kiev began in Ukraine's industrial heartland in April 2014.

Kiev and its Western allies accuse Russia of plotting and backing the conflict in order to keep its former Soviet neighbour in its historic sphere of influence.

Moscow denies the charges and accuses the United States of fomenting three months of bloody protests that brought down Ukraine's Russian-backed administration in February 2014.

The latest update on the human rights situation in the European Union's backyard came nine days after a UN torture prevention group suspended a visit to Ukraine because it was denied access to requested government detention sites.

"Enforced disappearances, arbitrary detention, torture and ill-treatment remain deeply entrenched practices, both in the territories controlled by the armed groups and in the territories controlled by the government," the report said.

Yet much of the criticism in the 53-page study was directed against the Kiev authorities and its SBU security service.

"Individuals detained by Ukrainian authorities in connection with the armed conflict have been tortured and ill-treated, and continue to face systematic violations of their due process and fair trial rights," the report said.

It accused the Ukrainian authorities of "restricting access to fundamental freedoms and socio-economic rights to persons living in the conflict-affected area."

The OHCHR said the self-declared leaders of the separatist Donetsk and Lugansk regions were also undermining the rights of the estimated 2.7 million people living under their control.

"They have imposed an arbitrary system of rules, established a network of places of deprivation of liberty where detainees are tortured and ill-treated, and cracked down on dissent," the report said.

There was no immediate response to the accusations from Kiev or the insurgents.

- Sexual violence -

"After two years of conflict, the human rights picture in eastern Ukraine remains extremely grim," UN assistant secretary-general for human rights Ivan Simonovic told reporters in Kiev.

"This crisis started with demands for human rights and freedoms, and these demands remain today on either side of the contact line."

Some of the most graphic details in the report describe cases of sexual and gender-based violence in both government and rebel-controlled regions.

A man detained by the insurgents in Donetsk said a militia commander tried to blackmail him into surrendering his house by threatening to rape his wife and daughters.

A woman arrested by Ukranian police described similar harassment.

"They asked me if I had given birth. When I replied 'yes, three times', they said that it meant I was able to endure pain," she was quoted as saying.

The police then "beat me with their fists and with a heavy flat object," she said.