The United Nations' Office of the High Commissioner for Human Rights on Monday warned of a "total breakdown of law and order and a reign of fear and terror" in eastern Ukraine.
A report released by the office detailed a range of trends, from widely reported abductions and detentions of civilians, to more elusive accounts such as forced labor and conscription.
Some abductions have been committed for ransom, and some have ended with executions, the report said, noting that at least 812 people have been detained or abducted since mid-April.
"Some abductions appear to be totally random," with teachers, journalists, students and members of the clergy among those taken, the report said.
The "intensified challenge to the government of Ukraine" on the part of the armed groups, which were left unnamed in the UN's statement, has resulted in heavier fighting all around and a general "collapse of the rule of law," the report said.
"Already increasing numbers of people are being killed with serious damage to civilian infrastructure, which depending on circumstances could amount to violations of international humanitarian law. The fighting must stop," the UN's high commissioner for human rights, Navi Pillay, was cited in the report as saying.
As of July 26, at least 1,129 people have been killed and another 3,442 wounded since mid-April, the report said.
The UN's monitoring mission also verified several reports of executions by armed groups, citing instances of armed groups holding "military tribunals" and issuing "execution orders" for people found to have violated their rules.
While the violence has so far been limited to Ukraine's restive east, the UN has also sounded the alarm over repercussions the conflict will have for the entire country.
"With the economic life of Donetsk and Luhansk now crippled, the impact on the rest of the country will be severe," the report said. On Monday, Ukrainian media cited Luhansk's city council as saying the area was completely without power after recent fighting damaged power lines.
Crimea, whose annexation by Russia earlier this year provoked international outcry, was also singled out in the report.
Those who opposed the controversial referendum to join Russia on March 16 have been harassed, the report said, as have members of religious minorities, Ukrainians and Crimean Tatars. This discrimination is likely to bring about a new wave of internally displaced persons fleeing the peninsula as new laws come into effect, the report said.