GENEVA — Hundreds of people have been killed and thousands have fled their homes amid rising violence, insecurity and crime in areas of eastern Ukraine that are under the control of pro-Russia armed groups, the United Nations said on Wednesday.

A total of 356 people are known to have been killed since mid-April, Gianni Magazzeni, a senior United Nations human rights official, told reporters in Geneva as he presented the latest in a series of monthly reports by the United Nations’ team of 34 monitors in Ukraine.

Fighting between the Ukrainian Army and armed groups in the eastern regions of Donetsk and Luhansk has increased in regularity and intensity as the government in Kiev seeks to assert its authority, and has led to a growing number of civilian casualties, the United Nations reported, noting that separatist groups have acknowledged that their ranks include fighters from Chechnya, a Russian republic, and elsewhere in the Caucasus.

The dead included 257 civilians and 86 Ukrainian military personnel, including the 49 who were killed last week when separatists shot down a military transport plane with a shoulder-launched missile as it approached Luhansk airport, Mr. Magazzeni said. The report did not offer additional details about the remaining 13 deaths.