The death toll from the February 22 explosion during a rally in the Ukrainian city of Kharkiv has risen to four, the Ukrainian interior minister's advisor Anton Heraschenko has said.

"At 5:00 a.m. today, Mykola Melnychuk, an 18-year-old student of Kharkiv's Municipal Economy Academy, died at the hospital from the terrible injuries sustained as a result this terrorist act. He became the fourth innocent Kharkiv resident who died at the hands of the Kharkiv Partisans terrorist organization," Heraschenko wrote on Facebook on Tuesday morning.

Another nine people injured in this "cynical and bloody terror act", which involved an anti-personnel mine, are still being treated at hospitals, he said.

An explosion ripped through the crowd attending Sunday's procession, which marked the first anniversary of the protests in Kyiv's Maidan, or Independence Square. Two people were killed instantly, and another one later died at the hospital.

A criminal investigation was opened on a count of terrorism (Article 258 of the Ukrainian Penal Code). The Ukrainian Security Service was put in charge of the inquiry.