The 36-page report singles out the Ukrainian far-right nationalist group Right Sector, which it claims has taken dozens of civilian prisoners as hostages, brutally torturing them and extorting large amounts of money from them and their families.
The report also mentioned widespread prisoner abuse by a wide array of captors on both sides of the conflict.
"More than 30 former prisoners held by both sides gave us consistent and harrowing accounts of their captors’ abuse", according to John Dalhuisen, the director of the Europe and Central Asia Program at Amnesty International.
He added that "prisoners on both sides have been beaten and subjected to mock executions".
The 33 people who were interviewed by Amnesty International so that it could get information about the torture included 17 who have been held by local militias in eastern Ukraine, and 16 who were detained by pro-Kiev military and law enforcement officials, including those from the Security Service of Ukraine.
The report revealed that in addition to being beaten and subjected to mock executions, former prisoners were also tortured with electric shocks, hung from the ceiling, deprived of sleep for days, threatened with death and denied urgent medical care.
The mission would include members of the Subcommittee on the Prevention of Torture and other Cruel, Inhuman or Degrading Treatment or Punishment as well as working groups on arbitrary detention and forced disappearances, according to Amnesty International.
In April 2014, Kiev launched its so-called anti-terror operation in eastern Ukraine, where two regions have declared autonomy; it claims the local militias who are defending the regions are supported by Russia, which vehemently denies the accusations.