Ukrainian and Russian authorities have been caught up for months in a struggle over Europe's largest nuclear plant. Now, Russian President Vladimir Putin has signed a decree that says his country will take operational control of the Zaporizhzhia complex. But the head of the International Atomic Energy Agency says the need for a safety zone there is "more urgent than ever."

Russian troops seized the plant in March. Ukrainian engineers kept it running even in the midst of shelling. Putin's decree says his Russia will "nationalize" the complex, a claim IAEA officials refuse to recognize.

IAEA Director General Rafael Grossi said, "We are not changing our line. We are continuing saying what has to be done which is basically to avoid a nuclear accident at the plant which is still a very, very clear possibility."

Two IAEA inspectors have been working onsite over the last month trying to assess the plant's safety. Grossi says two more will join them.

He met with Ukrainian President Volodymyr Zelenskyy on Thursday, a day after Putin signed the decree. Zelenskyy accused the Russians of "nuclear blackmail."

He said, "The main problem remains unresolved: the presence of soldiers at the nuclear plant. According to our information, which comes from the workers, there are around 500 Russians there. What do we do with this?"

Grossi has tried to persuade both sides to end fighting around the plant. He plans to visit Moscow to talk with Russian officials. However, he does not have the authority to order a ceasefire or to demand that troops leave the area.