Russia has summarily executed 77 civilians being held in arbitrary detention during its war in Ukraine, according to a United Nations report released Tuesday.

Since Russia began its invasion in February last year, the UN Human Rights Monitoring Mission in Ukraine has documented 864 individual cases of arbitrary detention by Russia, many of which also amounted to enforced disappearances.

"We documented the summary execution of 77 civilians while they were arbitrarily detained by the Russian Federation," Matilda Bogner, head of the mission, told a press briefing in Geneva.

These were 72 men and five women, while a further two male detainees died as a result of torture, inhumane detention conditions, and denial of medical care.

"Russian armed forces, law enforcement and penitentiary authorities engaged in widespread torture and ill-treatment of civilian detainees," said Bogner.

"Most of those we interviewed said they had been tortured and ill-treated, and in some cases subjected to sexual violence," which included rape.

"Torture was used to force victims to confess to helping Ukrainian armed forces, compel them to cooperate with the occupying authorities, or intimidate those with pro-Ukrainian views."

The report's findings were based on 1,136 interviews with victims, witnesses and others, plus 274 site visits and 70 visits to official places of detention run by Ukrainian authorities.

Overall, the report documented more than 900 cases of arbitrary detention of civilians, including children, and elderly people.

"The vast majority of these cases were perpetrated by the Russian Federation," said Bogner.

Ukraine gave the monitoring mission unimpeded confidential access to official places of detention and detainees, with one exception, while Russia did not grant such access despite requests, she said.

The mission documented 75 cases of arbitrary detention by Ukrainian security forces, mostly of people suspected of conflict-related offences.

A significant proportion of these cases also amounted to enforced disappearance, perpetrated mainly by the Security Service of Ukraine, said Bogner.

"We documented that over half of those arbitrarily detained were subjected to torture or ill-treatment by Ukrainian security forces. This happened while people were being interrogated, usually immediately after arrest," she said.

The mission did not document any summary executions of civilian detainees by Ukrainian forces. (AFP)

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