A report from the United Nations' human rights arm has strongly criticized both sides in Ukraine's fighting for the killing of civilians in indiscriminate shelling, as well as summary executions of both combatants and civilians.

The report released Thursday by the U.N.'s High Commissioner for Human Rights office says up to 2,000 civilians have died in the two-year conflict in eastern Ukraine between government forces and Russia-backed rebels, nearly 90 percent of them in shelling of residential areas.

The report also cited executions by both Ukrainian forces and rebel groups of "significant numbers" of people who allegedly were affiliated with or sympathetic to the other side.

Further, the report also claimed to have documented cases of Ukrainian servicemen intentionally killed for revealing abuses by Ukrainian forces.