A botched test at the nuclear plant triggered a meltdown that spewed deadly clouds of atomic material, forcing to the evacuation of tens of thousands of people.
Ukraine held memorial services on Tuesday to mark the 30th anniversary of the Chernobyl nuclear disaster, the worst in history.
Relatives of those who died as a result of the world's worst nuclear accident attended a candle-lit vigil in Kiev, others gathered for a service in Slavutych, a town 50 km from Chernobyl.
In the early hours of April 26, 1986, a botched test at the nuclear plant in then-Soviet Ukraine triggered a meltdown that spewed deadly clouds of atomic material into the atmosphere, forcing to the evacuation of tens of thousands of people.
More than 600,000 Soviet civilian and military personnel were drafted in from across the country as so-called liquidators to clean-up and contain the nuclear fallout.
"Chernobyl has become a serious lesson for all mankind, and to this day it has severe repercussions on both the environment and human health,” said on Tuesday Russian President Vladimir Putin in a telegram to the participants in the liquidation of the Chernobyl nuclear power plant disaster.
“The scale of the tragedy could be immeasurably greater, if it were not for the unprecedented courage and dedication of the firefighters, military personnel, experts, medical workers who honorably fulfilled their professional and civic duty," the president added.
Thirty-one plant workers and firemen died in the immediate aftermath of the accident, most from acute radiation sickness.
Over the past three decades, thousands more have succumbed to radiation-related illnesses such as cancer, although the total death toll and long-term health effects remain a subject of intense debate.