The United Nations said Monday that more than 6,400 people had been killed in conflict-wracked Ukraine, and despite a slowdown in fighting, millions more are suffering from abuses and hardship.
The UN human rights office also said there was increasing evidence that Russian servicemen are taking part in the hostilities.
In its latest report on the situation in Ukraine, the rights office said indiscriminate shelling had decreased significantly since a fragile truce was agreed in Minsk in February, resulting in fewer civilian casualties.
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But nonetheless, at least 6,417 people have perished from the beginning of the conflict in mid-April 2014 to May 30, 2015, while another 15,962 had been wounded, UN human rights envoy to Ukraine Ivan Simonovic told reporters.
He said the numbers were likely higher, since many people remain missing.
Some five million others are meanwhile suffering the consequences of the conflict, including 1.2 million people who have been displaced inside the war-ravaged country, the report said.
"Even with the decrease in hostilities, civilians continue to be killed and wounded," UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said in a statement, calling for the Minsk agreement to be fully implemented.
"We have documented alarming reports of summary executions by armed groups and are looking into similar allegations against Ukrainian armed forces," he said.
If confirmed, this "would represent clear evidence of war crimes," Simonovic said.
The report said civilians in areas controlled by armed groups faced "serious rights abuses" including killings, forced labor and extortion, while the government forces were slammed for using arbitrary and secret detention.
Zeid also lamented "horrific accounts of torture and ill-treatment in detention" by both sides.
One woman abducted and detained in rebel-held Donetsk last month had told the human rights investigators she was beaten, subjected to mock-executions and forced to play Russian roulette, and that another detainee was beaten to death in front of her, the report said.
Monday's report, which covers the period from mid-February to mid-May, stressed the shelling had not stopped altogether, and that combat between Ukrainian troops and pro-Russian armed groups was continuing.
Foreign fighters and heavy weaponry meanwhile was reportedly still flowing into the conflict-hit areas, and Simonovic said there was "increasing evidence" that some active Russian servicemen are also involved.
Observers from the human rights office interviewed two suspected Russian soldiers captured by Ukrainian troops last month, but Simonovic refused to provide details from the interviews.
It also warned that the conflict was taking a devastating toll on people's everyday lives, with vital services cut and some pensions and other sources of income dried up.
Since last December, the Ukrainian population has seen its real income plunge 8.4 percent, as prices have soared 20.3 percent and unemployment has reached 9.7 percent, the report said.
The IMF said on Sunday that Ukraine's war-battered economy was expected to contract nine percent this year.
"Millions of ordinary women, men and children in Ukraine have suffered tremendous hardship, violence and have been living in fear for more than a year now," Zeid said.
"Too many have had their homes and livelihoods destroyed and their lives torn apart, with no sign of justice, accountability, compensation or redress," he said, calling for the Minsk agreement to be fully implemented.
The report also slammed a system set up by Ukrainian authorities in January requiring that people fleeing rebel-held areas apply for a permit to enter areas under Kiev's control.
"Those seeking to obtain permits can face corrupt practices and delays of up to three months," it said.
Up until May 6, nearly 350,000 people had requested such permits, and nearly 275,000 had received them, according to Ukrainian security services, cited in the report.