Kyiv. The chief of Ukraine’s army said Tuesday that the country’s troops have gained control of nearly 1,300 square kilometers (500 square miles) of Russia’s Kursk region since their surprise incursion three weeks ago.

Gen. Oleksandr Syrskyi also said that Ukraine has captured 594 Russian prisoners in its operation. His claims could not be independently confirmed.

He said the Kursk incursion was drawing Russian troops from elsewhere, diluting them in some other areas. "They attempt to create a ring of defense around our offensive group of troops and plan counteroffensive actions,” Syrskyi said. The seized territory is roughly the size of Los Angeles.

Fighting in the region has raised concerns about dangers to the Kursk nuclear power plant, said International Atomic Energy Agency chief Rafael Grossi, who visited the plant on Tuesday.

“There is now a danger of a nuclear incident here,” Russian news agencies cited Grossi as saying. “Today I was told about several cases of drone attacks on the territory, on the plant’s facilities. At the plant I saw traces of these attacks."

But the plant now is operating “in a mode very close to normal," he said.

Syrskyi's claim of territorial control came hours after Ukraine endured a second consecutive barrage of nighttime air and missile attacks from Russia.

Five people were reported killed and 16 injured in the attacks, which President Volodymyr Zelensky said included 81 drones, as well as cruise and ballistic missiles. He said four people died, but the governor of the Zaporizhzhia region later said a fifth person had died there from burns in the attacks.

“We will undoubtedly respond to Russia for this and all other attacks. Crimes against humanity cannot go unpunished.” Zelensky wrote on X.

The Kursk operation, the largest incursion into Russia since World War II, has forced some 130,000 residents to evacuate their homes. Russia has sent reinforcements into the region, but it was not clear to what extent these movements might be weakening Russia's positions in Ukrainian territory.

Zelensky said Tuesday that Russia is not relocating troops to Kursk from Donetsk, the eastern Ukraine region that is the center of the war and where Russia has been making slow advances. However, Zelensky said the Kursk operation had prevented Russia's aims of taking territory in the Sumy and Kharkiv regions to the west of Kursk.

The Russian Defense Ministry said Tuesday that Ukraine has suffered heavy casualties in Kursk -- some 6,600 troops either killed or injured -- and that more than 70 tanks have been destroyed along with scores of armored vehicles. Those figures could not be independently confirmed.

In the Kyiv region, which had struggled with blackouts after Monday's onslaught that targeted energy facilities throughout the country, five air alerts were called during the night. The regional administration said air defenses destroyed all the drones and missiles but that falling debris set off forest fires.

After Monday's barrage across Ukraine of more than 100 missiles and a similar number of drones, Prime Minister Denys Shmyhal said "the energy infrastructure has once again become the target of Russian terrorists” and urged Ukraine’s allies to provide it with long-range weapons and permission to use them on targets inside Russia.

The allies “try not to speak with me about it. But I keep raising this topic. Generally, that’s it. The Olympics are over, but the ping-pong continues,” Zelensky said.

President Joe Biden called Monday's Russian attack on energy infrastructure “outrageous” and said he had “reprioritized US air defense exports so they are sent to Ukraine first.” He also said the US was “surging energy equipment to Ukraine to repair its systems and strengthen the resilience of Ukraine’s energy grid.”

The Russian Defense Ministry said the attacks used “long-range precision air- and sea-based weapons and strike drones against critical energy infrastructure facilities that support the operation of Ukraine’s military-industrial complex. All designated targets were hit.”

Russian officials reported four Ukrainian missiles were shot down over the Kursk region.