World leaders, nuclear power sceptics and survivors of the world's worst nuclear disaster gathered in Ukraine Tuesday to mark 30 years since the accident, and to ponder how much more damage could have resulted from the 1986 Chernobyl meltdown.
"Chernobyl led to a leap forward in global cooperation on nuclear safety," said Yukiya Amano, head of the International Atomic Energy Agency (IAEA), as the world reflected on a disaster whose reverberations can still be felt to this day.
Ukrainian President Petro Poroshenko laid a wreath of flowers at a memorial to Chernobyl in Kiev on Tuesday, the 30th anniversary of the disaster.
The country's new prime minister, Volodymyr Groysman, and parliament speaker Andriy Parubiy, who were both appointed this month, attended the ceremony, according to a statement on Poroshenko's website.
Poroshenko was scheduled later in the day to attend a ceremony at the site of the disaster, in northern Ukraine's Exclusion Zone, near the Belarusian border.
Representatives of the European Bank for Reconstruction and Development (EBRD) and 28 countries that have contributed funds for the decontamination will attend the ceremony, according to a statement on the Exclusion Zone's website.
The international community has contributed more than 2 billion euros to cleaning up and preventing further contamination at Chernobyl, according to the European Commission.
The key lesson from Chernobyl and the 2011 nuclear disaster in Fukushima, Japan, was that governments, authorities and nuclear plant operators must not take safety for granted, said Amano.
"Complacency must be avoided at all costs," he said in Vienna.
After the accident, countries began sharing safety know-how, and have since adopted a set of rules called the Convention on Nuclear Safety and set up a process to review each other's safety record.
Russian President Vladimir Putin expressed his condolences for the tragedy, in a statement on the Kremlin's website.
"Chernobyl was a serious lesson for all of humanity," Putin said.
On April 26, 1986, a malfunction during a system test of the plant's Reactor Number 4 set off a series of explosions that sent thousands of tons of radioactive material into the atmosphere.
About 100,000 residents were evacuated from the surrounding area in what were then the Soviet republics of Ukraine and Belarus, while about 600,000 Soviet workers strove to decontaminate the territory and erect a "sarcophagus" of lead and concrete to contain the radiation within the damaged reactor.
The sarcophagus, which was built in a rush, was never intended as anything other than a temporary solution. A new steel-based structure, the "New Safe Confinement," is being built to better enclose the reactor.