An 18-year-old student has become the latest victim of the bomb blast that rocked Ukraine’s second-largest city of Kharkiv on Sunday. The student died Tuesday morning from head wounds sustained from the bomb attack, which Ukrainian officials blame on pro-Russian rebels.

"He was the fourth innocent Kharkiv citizen to die at the hands of the Kharkiv guerrilla-terrorist organization," Anton Herashchenko, an adviser to the Interior Ministry, wrote on his Facebook page, using the Kiev government's term to describe pro-Russian separatists. 

The blast took place during a peace march to mark one year since the overthrow of Ukraine President Viktor Yanukovych. Police Lt. Col. Vadym Rybalchenko and activist Igor Tolmachev were killed at the scene. A 15-year-old boy was taken to a hospital but died from severe head injuries.

Since the blast, Ukrainian authorities have said on social media that they have found more bombs around the city and made additional arrests, blaming pro-Russian rebels.

Deaths in the conflict, including from fighting in the port city of Mariupol and around Donetsk, have risen to around 5,800 since the war began in April 2014, including 63 children, according to a U.N. report released Monday. Another 14,500 people have been wounded, said the report.

The fighting continues despite a ceasefire that was signed on Feb. 12 and supposedly came into force on Feb. 15.

The Organization for Security and Co-Operation in Europe, the international organization charged with monitoring the ceasefire, has faced increased hostility from the rebels, including death threats, said an OSCE report. "The local commander of the 'DNR' at the checkpoint threatened to kill the mission representatives," the report said, referring to the self-proclaimed Donetsk People's Republic. The OSCE also said a drone "attempting to monitor compliance with the Minsk Package in the environs of the Donetsk airport was consistently jammed." The Minsk Package is the list of measures agreed to in the ceasefire, including the withdrawal of heavy artillery and soldiers beyond a certain line.