The Soviet Union knew the Chernobyl nuclear plant was unsafe and covered up emergencies there before the 1986 disaster, Ukrainian authorities said on Monday as they released documents commemorating the accident’s 35th anniversary.

Following a failed safety test in the plant’s fourth reactor, located in what was then Soviet Ukraine, clouds of radioactive material from Chernobyl dispersed over most of Europe, resulting in the world’s worst nuclear disaster.

According to the archives, there was a radiation leak at the plant in 1982 that was covered up using what a KGB article at the time referred to as steps “to prevent panic and provocative rumours,” Ukraine’s security service (SBU) said in a statement.

There were separate “emergencies” at the plant in 1984, it added, Reuters reports.

“In 1983, the Moscow leadership received information that the Chernobyl nuclear power plant was one of the most dangerous nuclear power plants in the USSR due to lack of safety equipment,” the SBU said.

The Soviet Union knew the Chernobyl nuclear power plant was unsafe and covered up emergencies there before the 1986 disaster, Ukrainian authorities said on Monday as they released documents commemorating the accident’s 35th anniversary.

After a failed safety test in the plant’s fourth reactor, located in what was then Soviet Ukraine, clouds of radioactive material from Chernobyl dispersed over most of Europe in what remains the world’s worst nuclear disaster.

According to the archives, there was a radiation leak at the plant in 1982 that was covered up using what a KGB study at the time called steps “to prevent panic and provocative rumours,” Ukraine’s security service (SBU) said in a statement.

“The 35th anniversary of the Chernobyl tragedy is a reminder of how state-sponsored disinformation, as propagated by the totalitarian Soviet regime, led to the greatest man-made disaster in human history,” the foreign ministry said.

More stories: