"Authorities largely failed to investigate these deaths," the report said, of 48 people who died in a fire at the Trade Union Building in Odessa in May 2014.
Investigations into the 2014 Euromaidan shootings in Kiev and deaths in Odessa remained incomplete more than a year later, the report noted.
In February 2014, violent clashes between protesters and law enforcement broke out in central Kiev's Independence Square, or Maidan Nezalezhnosti, claiming the lives of some 100 people. The protests led to a government coup, forcing then-President Viktor Yanukovych to flee the country.
On May 2, 2014, pro-Kiev radicals blocked anti-government protesters in Odesa's House of Trade Unions and set the building on fire by hurling Molotov cocktails inside. Forty-eight people died in the incident and more than 250 were injured.