Both sides of the conflict in Ukraine are guilty of indiscriminately shelling civilian areas and carrying out summary executions of both combatants and civilians, according to a new report released by the United Nations.

The two-year conflict in eastern Ukraine between government forces and Russian-backed rebels has killed up to 2,000 civilians, nearly 90 percent of them in the shelling of residential areas, the report released by the office of the the UN High Commissioner for Human Rights (OHCHR) said on Thursday.

The report also cites executions by both Ukrainian forces and rebel groups of "significant numbers" of people.

The victims of execution include people allegedly affiliated with or sympathetic to the opposing side, as well as combatants who had surrendered or were out of action.

"There needs to be a strong investigation in order to identify perpetrators of crimes committed, to bring justice to the victims and their families to end the continued suffering, and at the end of the day to ensure there is accountability in this country," Fiona Frazer, head of the UN human rights monitoring mission for Ukraine, told The Associated Press.

The report said that the majority of the incidents in question happened in late 2014 and early 2015.

A Ukrainian foreign ministry statement said the country "highly values" the work of UN human rights monitors in the country, but it focused blame on the rebels.

The ministry claimed that the report found the majority of civilian deaths was due to rebel artillery and said Ukrainian forces are banned from firing on rebel positions near civilian areas.

'Killed for revealing abuses'

The report claimed to have documented cases of Ukrainian servicemen intentionally killed for revealing abuses by Ukrainian forces.

The series of alleged crimes committed by Kiev's troops include one in which two suspected rebels were kept in a dry well and then killed by "a drunken soldier" who threw a grenade down the shaft.

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The 26-month revolt against the pro-Western government in Kiev has killed nearly 9,500 people and plunged Moscow's ties with the West into a post-Cold War low, which has complicated the resolution of other urgent matters such as the war in Syria.

The Kremlin has repeatedly denied either plotting or backing the rebels in Ukraine in order to keep its western neighbour within a post-Soviet sphere of influence.

The exhaustive study into the Ukrainian conflict by OHCHR was conducted between January 2014 and May of this year.

Its report also noted that no arrests have been made in the shooting dead of 13 policemen in the capital Kiev during the final days of the massive street protests that drove Ukraine's Russia-friendly president to flee.

The human rights office also said that it was concerned that authorities hadn't conducted an effective investigation into the deaths of 48 people in the city of Odessa on a day of clashes in 2014 between supporters of the new pro-Western Ukrainian government and their opponents. Forty two of those died in a fire at a building where anti-government demonstrators had taken shelter. Many believe the blaze was started by firebombs thrown into the building.