Radiation levels near the Chernobyl plant are within safe limits, the nuclear agency chief says.

Radiation levels are elevated in some parts of the soil near the defunct Chernobyl nuclear plant in northern Ukraine, but do not pose a significant threat to workers or the environment, the head of the international nuclear watchdog agency said on Thursday.

Rafael Mariano Grossi, director general of the International Atomic Energy Agency, made the assessment on the basis of readings taken at the site this week, after the first visit by nuclear inspectors since Russian forces withdrew from Chernobyl in late March.

In 1986, Chernobyl was the site of the world’s worst nuclear accident, caused by an explosion and fire at a reactor. The facility was subsequently closed and secured, but concerns about the safety of the site rose when it was seized by Russian forces shortly after their invasion of Ukraine on Feb. 24.

Those forces dug up a section of earth outside the plant, apparently as part of a military operation, raising fears that they could have inadvertently released some radioactive material.

“There was an increase” in radiation levels at the place where Russian forces dug, Mr. Grossi said at a news conference at the agency’s headquarters in Vienna. “But this increase is still significantly below the authorized levels for workers in an environment with this type of radiation.”

Mr. Grossi said that one purpose of his visit to Chernobyl on Tuesday was so that his team could repair connectivity between the site and the agency’s headquarters in Vienna, and restore continuous monitoring.

Mr. Grossi said his chief concern in Ukraine was the Zaporizhzhia plant in the southeast, the largest nuclear facility in Europe, because it has remained under Russian control since the Kremlin’s forces took the area in March. Ukrainian regulators and experts have been unable to perform inspections or assess the state of safety equipment, he said.

In a report released Thursday that summarized the situation, Mr. Grossi’s agency said 10 senior technical officials from Russia’s atomic energy agency, Rosatom, had remained on the Zaporizhzhia site since the Russian military took it over, raising the risk of interference with the Ukrainian staff and “potential frictions when it comes to decision-making.”

The report said the morale and emotional state of the Zaporizhzhia plant’s Ukrainian staff had been “very low since the Russian military forces seized the site.” It added that Mr. Grossi regarded the situation as “unacceptable and unsustainable.”

Rick Gladstone contributed reporting.