Rafael Mariano Grossi, Director General of the IAEA, said that radiation levels were normal and that he was standing under an umbrella while it rained outside the nuclear power plant.
Russian troops moved into the radiation-contaminated Chernobyl exclusion zone in February on their way toward the Ukrainian capital. They left in late February after Russia withdrew its forces from Kyiv, and the focus shifted to fighting for eastern Ukraine.
Since then, the site is back in Ukrainian hands and all disrupted communications have been restored.
According to Ukrainian officials, the Russian occupiers kept plant workers under gunpoint for more than a month. They also slept on tablets and ate only twice daily.
Grossi congratulated workers for reducing potential risks during occupation, which included power disruptions.
He said, "I don’t know if it was very close to disaster but the situation had been absolutely abnormal and very, very risky."
Volodymyr Zelenskyy of Ukraine, remarking on the Chernobyl anniversary via Twitter, stated that "not everybody realized" the dangers associated with nuclear energy.
"Russia's actions at the Ukrainian nuclear power stations threaten humanity with a new disaster."
The April 26, 1986 explosion at Chernobyl and subsequent fire created radioactive material in the atmosphere. This was the symbol of the Soviet Union's final years. Russia was part of the international community that spent billions to secure and stabilize the region.
The unit that caused the fire and explosion was covered in a high-tech encasement. However, the dangers to the plant continue because spent nuclear fuel rods require round-the-clock maintenance. The plant has four reactors that are now all shut down.
Russian forces still control a functioning nuclear power plant in the southern Ukraine, Europe's biggest, which is held by them. In March, fighting destroyed the Zaporizhzhia training facility.
A reporter from the Associated Press visited Chernobyl in March and saw evidence that Russian soldiers had dug trenches within the Chernobyl exclusion area in the early hours of the invasion. This was churning up highly contaminated soil.
IAEA staff members were on Tuesday at Chernobyl to do repairs and assessments. They brought black suitcases with them from their vans. Grossi stated that they were carrying dosimeters, and other radiation monitoring equipment.
He stated that there is still a lot to do after the occupation of the plant. "We need to repair the connection that we have with Vienna so we can give good information to the Ukrainian people and to the rest of world.
Austria's capital is home to the International Atomic Energy Agency. It is the world's leading nuclear watchdog.
Chernobyl lost normal electricity supply during the Russian occupation. Diesel generators were used by plant workers to provide power for the vital work of cooling spent nuclear fuel with circulating water.
Grossi was asked if the Russian occupation posed the same dangers as the one following the original Chernobyl disaster. Grossi responded: "On that occasion you had an explosion, and you had an operational reactor. It was completely different. This was an unusual situation, and could have led to an accident.
Grossi responded to concerns expressed by the public about nuclear power in wars. He said that the problem wasn't nuclear energy. The problem is war.