A mine sweep by the International Atomic Energy Agency is “making progress” and no explosives have been found so far, director general Rafael Grossi said on Friday.
But he said the agency's staff had yet to get access to the rooftops of reactor units 3 and 4 which it had requested two days ago.
“I'm pretty confident that we will get this authorisation,” Mr Grossi said.
“This is a combat zone, it's an active war zone, so sometimes it may take a day or two to get the authorisations.”
He said “tours of the cooling ponds and other places” did not turn up any indications of mines or explosives.
The warring sides have accused each other of planning a provocation at the Ukrainian plant occupied by Russian troops.
Ukraine's President Volodymyr Zelenskyy said “objects resembling explosives” were placed on the roof by Russian forces. He suggested they were there to “simulate an attack on the plant”.
Russia denied this and said there was a “great threat of sabotage” by Ukraine.
Fears of a disaster at Zaporizhzhia have persisted since Russia occupied the plant in the early stages of the invasion last year. The two sides have blamed each other for shelling near the plant while a dam breach on the Dnipro River added to concerns about cooling the site's six reactors.
Mr Grossi has said the world is fortunate to have avoided a disaster and warned in March that “one day our luck will run out”.
Ukraine's military meanwhile said Russian troops in the Zaporizhzhia region were using children's homes to accommodate troops.
It claimed more than 800 Russians had set up a base in a children's infirmary in Novopetrivka and stationed military equipment nearby.
Mr Zelenskyy has raised the nuclear threat at Zaporizhzhia in meetings with Nato leaders before the alliance holds its main annual summit in Lithuania next week. Ukraine is seeking progress on its membership bid that some western allies are reluctant to provide.
The European Union announced a deal early on Friday to find €500 million ($544.2 million) in its budget to support ammunition production that could go to Ukraine.
“This is yet another proof of the EU’s unwavering commitment to supporting Ukraine,” said Spain's Defence Minister Margarita Robles, whose country holds the bloc's rotating presidency.