A UN monitoring mission in Ukraine said on Tuesday that Russia has detained more than 800 civilians since the conflict began last February, of whom 77 were executed.
The report showed that Ukraine had also violated international law by arbitrarily detaining civilians but on a considerably smaller scale.
"(The UN rights office) identified patterns of conduct which have resulted in arbitrary detention, as well as further human rights violations including torture, ill treatment and enforced disappearances," the report said, adding that the detentions by Russia had taken place in both Ukraine and Russia.
"While such conduct was found in relation to both parties to the conflict, there was greater prevalence of conduct attributed to forces of the Russian Federation."