On May 2, 2014 pro-Kiev radicals and Right Sector blocked a group of anti-government protesters in Odessa's House of Trade Unions and set the building on fire, using Molotov cocktails.
At least 48 people died, including several who jumped to their deaths in an attempt to escape, and over 200 were injured as a result of the fire.
The organizers of the event passed on an appeal to the Ukrainian diplomats.
"In the appeal, there is a request for an investigation which has not been conducted yet, and to punish the perpetrators," one of the organizers, Irina Bomatova, told RIA Novosti.
Local officials accused Kiev of covering up the actual death, claiming that at least 116 had been killed.
Moscow has repeatedly urged Kiev to conduct a prompt and transparent investigation into the Odessa tragedy since the day of the deadly fire.
One year after the tragedy, Kiev authorities have not completed the investigation of the case and perpetrators have not been brought to justice.