Ukrainian President Volodymyr Zelenskiy said Russia must take responsibility for an "act of terror" after Kyiv and Moscow traded blame for strikes at the Zaporizhzhya nuclear plant in Ukraine.

"Today, the occupiers have created another extremely risky situation for all of Europe: they struck the Zaporizhzhya nuclear power plant twice. Any bombing of this site is a shameless crime, an act of terror," Zelenskiy said in his nightly video address.

"Russia must take responsibility for the very fact of creating a threat to a nuclear plant," he said.

The world's response should be harsh sanctions against the entire Russian nuclear industry from Rosatom to all related companies and individuals, he added.

Ukraine's Energoatom state nuclear power company said earlier that a high-voltage power line at the Zaporizhzhya nuclear power plant had been hit by Russian shelling.

The statement said the plant was still operating and no radioactive discharges had been detected. It said one reactor had been disconnected from the network because of damage to the high-voltage power line.

The statement came shortly after the Russian-installed administration of the occupied Ukrainian city of Enerhodar, where the plant is located, said power lines at the plant had been damaged by a Ukrainian artillery strike.

The Interfax news agency cited the city administration as saying fire had broken out on the plant's premises, and that power necessary for the safe functioning of reactors had been cut off.

The power plant, located about 200 kilometers northwest of the Russian-held port of Mariupol, has been under Russian supervision since Moscow's troops seized it early in the war.

The Russian Defense Ministry also accused the Ukrainian Army of striking the power plant.

"Ukrainian armed units carried out three artillery strikes on the territory of the Zaporizhzhya nuclear power plant and the city of Enerhodar," the ministry said in a statement.

As a result of the strikes, a hydrogen pipeline was damaged, leading to a fire, the ministry said, adding that the blaze was quickly extinguished.

It claimed that a leak of radiation had been avoided only by luck and said the generating capacity of one unit had been reduced and power supply to another had been cut.

In addition, the city of Enerhodar had problems with power and water supplies, the ministry statement said.

The statement said Zelenskiy's government was committing acts of "nuclear terrorism" and urged international organizations to condemn the actions.

Valentyn Reznichenko, the regional governor in Dnipropetrovsk, said that Russian forces shelled a city across the Dnieper River from the plant the day before.

Reznichenko said Russia fired 60 rockets at Nikopol, damaging around 50 residential buildings and leaving some residents without electricity.

Military experts quoted in U.S. media reports say they believe Russia is shelling the area intentionally, knowing that Ukrainian forces cannot risk returning fire because it could damage the reactors or disturb nuclear waste sites.

The shelling has already caused concern at the UN’s nuclear watchdog.

Rafael Grossi, director-general of the International Atomic Energy Agency (IAEA) said on August 3 that “every principle of nuclear safety has been violated” at the plant. “What is at stake is extremely serious and extremely grave and dangerous,” Grossi said.

Britain's Ministry of Defense said in its daily intelligence bulletin on August 5 that Russia's intentions toward the nuclear plant remain unclear.

However, the bulletin noted, the actions that the Russians have undertaken at the facility have "likely undermined the security and safety of the plant’s normal operations."

Elsewhere on the battlefield, more than 10 people were injured and an unknown number of people were killed as a result of the shelling of Mykolayiv, Vitaliy Kim, the head of the regional military administration, said on Telegram.

Kim warned earlier that a curfew would be introduced on the territory of Mykolayiv from 11 p.m. on August 5 to 5 a.m. on August 8. He urged people to take appropriate measures, adding that three evacuation buses would be leaving the city accompanied by a police escort.

Fierce fighting was under way in Ukraine's eastern region of Donetsk, while Ukrainian military officials said Russia may launch a fresh offensive in the south

Ukraine's second-largest city, Kharkiv, was shelled by the Russians, Ukraine's presidential office said.

Several industrial sites were hit in the city, and in the nearby city of Chuhuiv a rocket hit a five-story residential building.

Ukrainian forces successfully fought off Russian attacks northeast and east of the Donetsk region towns of Soledar and Bakhmut, while fighting was ongoing to the south of Bakhmut, Brigadier General Oleksiy Hromov, deputy chief of the Ukrainian General Staff, said on August 4.

However, Hromov confirmed that Ukrainian troops had been forced to withdraw from the village of Semyhirya and their positions southeast of Avdiyivka.

Hromov told a news conference that Ukrainian forces had recaptured two villages around the eastern city of Slovyansk but had been pushed back to a nearby town after being forced to abandon a coal mine regarded as a key defensive position.

He said Moscow may launch an offensive in the southern Ukrainian region of Kherson to try to win back momentum in the war and it has been building up forces there.

With reporting by Reuters, dpa, and AP