Pro-Russian rebels have imposed a reign of fear in eastern Ukraine, abducting scores of real and imagined opponents and subjecting them to torture, the UN human rights office said on Wednesday.
In a fresh report by its monitors in the conflict-torn country, the UN office also said hundreds had perished in fighting and that the rights situation had worsened since it took stock in early May.
"The main problem is in the areas controlled by armed groups," said Gianni Magazzeni, a senior official with the Office of the High Commissioner for Human Rights (OHCHR).
"We have a situation of a reign of fear, if not terror, for those that are caught in those specific locations," he told reporters.
Ukraine launched an offensive in April in an attempt to take back rebel strongholds.
Since then, Magazzeni said, at least 356 people have been killed. The number was based on a mix of official data and research on the ground.
A total of 86 of the dead were Ukrainian servicemen, including 49 whose transport plane was shot down on June 14.
Magazzeni said the figure of 270 non-military fatalities included both rebel fighters and civilian victims.
The rebels seized control of the strategic southern province of Crimea and various other mainly Russian-speaking communities in the east after the February ouster of Moscow-tied president Viktor Yanukovych.
Russia has faced international condemnation for annexing Crimea. Tens of thousands of people, mostly Muslim Tatars, have been displaced from the region.
Moscow rejects the criticism, as well as charges of sending arms and men to the rebels in areas such as the city of Donetsk.
In a statement on Wednesday, the Russian foreign ministry lambasted the OHCHR report as "politically one-sided".
"The attempt to place without proof all responsibility for the bloodshed in eastern Ukraine on the militia of Donetsk and Lugansk is unacceptable," it said.
It claimed that Ukraine was meanwhile being handed an excuse to "continue to exterminate the civilian population and escalate the conflict".
Beatings, forced labour, killings
The OHCHR did not tackle the issue of Moscow's role head-on, but noted that the self-declared Donetsk People's Republic had acknowledged the presence of Russian citizens within its forces.
In Donetsk and the rebel bastion Lugansk, at least 222 people have been abducted, among them monitors from the Organisation for Security and Cooperation in Europe, Magazzeni said.
At least four people are known to have been summarily executed and 137 have been released, he said.
The whereabouts of the remaining 81 detainees is unknown, he added, noting that testimony from freed individuals raised fears for their fate.
"Some of those released talked about beatings, sleep deprivation, poor or inhumane conditions, sometimes forced labour, including requests from the so-called de facto authorities and armed groups to join their ranks and eventually be used to abduct more people," he said.
"People have been killed at checkpoints for no reason other than perhaps not slowing down promptly, or shot because they have brought food to servicemen, or been shot by armed groups because they no longer wanted to fight," he added.
The rebels insist they took up arms to defend ethnic Russians against the Right Sector, a hardline group within the movement that ousted Yanukovych.
Previous OHCHR reports have rejected that argument, and Magazzeni reaffirmed the point.
"The so-called Right Sector is very small," he said, noting that it mustered two percent of the vote in May's Ukrainian presidential election.
"The inability of minorities to be respected is not an argument that we see in day-to-day life or we see corroborated by evidence on the ground," he added.
Magazzeni noted that Ukraine's new government had swiftly voided legislation restricting the official use of Russian, as well as launching moves to decentralise power.