The Kremlin on Monday denied that its forces were responsible for large-scale killings in eastern Ukraine and accused Kyiv of fabricating its discoveries of mass graves in retaken areas.

In the latest incident, which stoked fears of a nuclear emergency, Ukraine said Russian missiles landed dangerously close to a nuclear power plant in southern Ukraine.

Ukraine this month retook Izyum and other cities in the east, crippled the Kremlin’s supply routes and made new claims of Russian atrocities with the discovery of hundreds of graves, some containing multiple bodies.

“These are lies,” Kremlin spokesman Dmitry Peskov told reporters on Monday. Moscow, he said, “will stand up for the truth in this story.”

Fighting raged in the north-east and AFP journalists heard artillery fire on the Kupiansk frontline on Monday as traumatized civilians, now mostly in the hands of Ukrainian forces, left the city.

The streets were littered with broken glass, spent bullet casings and the discarded remnants of ration packs issued by both forces.

Most of the fire dies down, with Ukrainian tanks and artillery targeting Russian positions on the west side of the city, across a jumble of ruined bridges. A column of smoke rose in the distance.

Civilians gathered at the entrance to the city, cowering to the sounds of Ukrainian tank shells flying overhead toward Russian lines to hitchhike or join buses to head to safer Ukrainian territory.

“There has been no light, no electricity for a week. No water,” said a 49-year-old former police officer, who only gave his name as Ruslan.

Russian-backed authorities in eastern Ukraine said a “punitive strike” by Kiev forces killed more than a dozen people and injured others in the separatist stronghold of Donetsk.

The region’s rebel leader claimed the strike was “premeditated” and said it “will not go unpunished”.

A court in the neighboring rebel region of Lugansk has sentenced an employee of the Organization for Security and Cooperation in Europe to 13 years in prison for disclosing military secrets.

Months of brutality under Russian occupation have been reported by Ukrainian civilians in the recaptured northeastern Kharkiv region.

In Kupyansk, Mykhailo Chindey told AFP he was tortured on suspicion of supplying target coordinates to Ukrainian forces.

“One person held my hand and another hit my arm with a metal stick. They beat me for two hours almost every day,” he told AFP.

“At one point I lost consciousness. I lost a lot of blood. They hit my heels, my back, my legs and my kidneys,” he said.

Ukraine’s atomic energy agency Energoatom said Russia hit the Pivdennoukrainsk nuclear power plant overnight with a “powerful explosion” just 300 meters (985 feet) from its reactors.

The strike damaged more than 100 windows at the station, but the reactors were not damaged, Energoatom said, posting photos of broken glass around blown frames.

It also released images of a crater said to be two meters deep, from which the rocket landed. No staff was injured, it said.

Attacks on Ukraine’s nuclear facilities have prompted calls from Ukraine and its western allies for the demilitarization of surrounding areas.

Europe’s largest nuclear facility – the Zaporizhzhia nuclear power plant on Russian-held territory in Ukraine – has become a focus of concern after the attacks against each other were negotiated.

The United Nations nuclear agency dispatched a surveillance team to the site in early September after renewed fighting.

At the start of the invasion in February, fighting broke out around Chernobyl in the north, where a 1986 explosion contaminated much of the surrounding territory.

“Russia endangers the whole world. We have to stop it before it’s too late,” President Volodymyr Zelenskyy said early Monday.

French President Emmanuel Macron this month called on Vladimir Putin to withdraw Russian heavy weapons from Zaporizhia. The Russian leader warned of possible “catastrophic” consequences of the fighting there.

The Mykolaiv region of southern Ukraine, where the Pivdennoukrainsk plant is located, lies close to the front line of a southern Ukrainian counter-offensive.

Kyiv’s forces have retaken territory near Mykolayiv and are approaching the strategic hub of Kherson.

Russian forces have continued to shell Ukrainian-held towns near the front lines.