NIKOPOL, Ukraine (AP) — Russian shelling across the river from Ukraine's main atomic plant wounded four people on Monday, an official said, only hours after the latest international pleas to spare the area from attacks to prevent a nuclear disaster.

And as danger and fear spread ever further beyond the front lines in eastern and southern Ukraine, Russia's top counterintelligence agency accused Ukrainian spy agencies have organized the killing in Moscow of the daughter of a Russian nationalist ideologue.

On the battleground itself, Nikopol, about 10 kilometers (six miles) downstream from the Zaporizhzhya nuclear plant, came under fire three times overnight from rockets and mortar shells, hitting houses, a kindergarten, the bus station and stores.

Mayor Oleksandr Saiuk said four people were wounded, including two who were hospitalized.

Reports of sustained shelling around Europe's largest nuclear power plant further highlighted the dangers of a war that will hit the half-year mark on Wednesday.

After U.N. Secretary General Antonio Guterres again urged caution during a visit to Ukraine last week, U.S. President Joe Biden further discussed the issue with the leaders of France, Germany and Britain on Sunday.

The four leaders stressed the need to avoid military operations in the region to prevent the possibility of a potentially devastating nuclear incident and called for the U.N.'s atomic energy agency to be allowed to visit the facilities as soon as possible.

But nothing seemed certain in a war that has spread into the Russia-annexed Crimea Peninsula and as far as Moscow, where on Saturday night a car blast killed the daughter of an influential Russian political theorist often referred to as "Putin's brain."

On Monday, Russia's Federal Security Service (FSB), the main KGB successor agency, said that the killing of Darya Dugina has been "prepared and perpetrated by the Ukrainian special services." It charged that the killing was perpetrated by a Ukrainian citizen, who left Russia for Estonia after the killing.

The FSB said that the suspect, Natalya Vovk, rented an apartment in the building where Dugina lived and shadowed her. Vovk and her daughter were at a nationalist festival, which Alexander Dugin and his daughter attended just before the killing. Ukraine officials earlier have denied involvement.

In Crimea, anxiety has spread further following a spate of fires and explosions at Russian facilities over the past two weeks. The governor of Sevastopol, Mikhail Razvozhaev, ordered that signs showing the location of bomb shelters be placed in the city, which had long seemed untouchable.

Monday's statement follows a series of drone incursions into Sevastopol, which is home to Russia's Black Sea Fleet. A drone exploded at the fleet's headquarters on July 31 and another was shot down over it last week. Authorities also say air-defense systems have shot down other drones.

Razvozhaev said on Telegram that the city is well protected, but "it is better to know where the shelters are."

Russian President Vladimir Putin didn't mention Russia's military operation in Ukraine during a speech marking National Flag Day on Monday, but echoed some of the justifications cited for sending in troops.

"We are firm in pursuing in the international arena only those policies that meet the fundamental interests of the motherland," Putin said. He maintains that Russia sent troops into Ukraine as effectively a protective measure against the encroaching West.

"The desire to live according to one's will, to choose one's own path and follow it, has become part of the genetic code of our people," he said.

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