The head of the U.N.'s atomic energy watchdog returned Wednesday to the Zaporizhzhia Nuclear Power Plant, a day after saying a deal to protect Europe's largest nuclear power facility from a catastrophic accident due to the war in Ukraine was "close."

International Atomic Energy Agency Director General Rafael Mariano Grossi crossed the war's front lines for a second time to reach the plant, which is located in a partially Russia-occupied part of Ukraine where combat has intensified.

The IAEA, which is based in Vienna, Austria, has a rotating team permanently based at the plant. Grossi told The Associated Press in an interview Tuesday he feels it is his duty to ramp up talks between Kyiv and Moscow aimed at safeguarding the facility.

He met Monday with Ukrainian President Volodymyr Zelenskyy and said he would "most probably" head to Moscow in the coming days.

However, Zelenskyy said in a separate interview with the AP that he was less optimistic a deal was near. "I don't feel it today," he said.

The Kremlin's forces took over the six-reactor plant after Russia's full-scale invasion in February 2022, and Zelenskyy opposes any proposal that would legitimize Russia's control over the facility.

Grossi repeatedly has urged Zelenskyy and Russian President Vladimir Putin to allow a protection zone around the plant, which is very near the front line of the war.

The negotiations are specific to preventing a nuclear disaster at the plant and not aimed at securing a broader cease-fire, Grossi told the AP.

The power station's reactors are shut down and the plant has received the electricity it needs to run the cooling systems needed to prevent a reactor meltdown through one remaining functioning power line.

Interruptions to the outside electricity supply due to the fighting required plant personnel to switch to emergency diesel generators six times during the 13-month war. When backup power supplies might be needed again is unpredictable, according to Grossi.