Five years after 48 people died in clashes in the Ukrainian city of Odessa, including dozens in a burning building, the U.N. human rights monitoring mission in the country is criticizing authorities for delays in prosecution and investigation of the violence.

The violence started in a confrontation between demonstrators calling for autonomy for eastern Ukraine where a Russia-backed separatist uprising had begun, and demonstrators supporting Ukraine's government. Six people died in that clash.

Pro-autonomy demonstrators retreated to a trade union building. Government supporters threw fire bombs into the building; 42 people died inside or from jumping or falling from windows.

In a statement on the bloodshed's five-year anniversary, the monitoring mission said Thursday that "authorities have not done what it takes to ensure prompt, independent and impartial investigations and prosecutions."