"Since the conflict began in eastern Ukraine in mid-April 2014, a total of at least 7,962 people... Have been killed," and at least 17,811 have been injured, the office said in its latest report.
Covering the period from May 16 to August 15, the report noted a particular rise in the number of civilians killed or injured.
"Civilian casualties more than doubled by comparison with the previous three months, with at least 105 people killed and 308 injured compared to 60 killed and 102 injured between 16 February and 15 May," it said.
By contrast, pro-Russian separatists were making no attempts to implement the agreement and were persisting with efforts to establish parallel -- and illegal -- state structures in areas under their control, it said.