KYIV, May 22 – A group of Russian citizens fighting as a unit on the side of Ukraine has crossed the border into Russia on Monday, quickly advancing to take control over three small settlements in the Belgorod region.

Ukraine intelligence representative Andrii Cherniak said Russian citizens belonging to groups calling themselves the Russian Volunteer Corps and the “Freedom of Russia” Legion were behind the assault.

The governor of Russia’s Belgorod region, which borders Ukraine, said that a Ukrainian Armed Forces saboteur group entered the town of Graivoron, about five kilometers (three miles) from the border, The Associated Press reported. The town also came under Ukrainian artillery fire, he said.

President Volodymyr Zelenskyy’s advisor, Mykhailo Podolyak, said on Twitter that Ukraine “has nothing to do with it.” He suggested an “armed guerrilla movement” was behind the attack.

The Russian Volunteer Corps claimed in a Telegram post it had crossed the border into Russia again, after claiming to have breached the border in early March.

The Russian Volunteer Corps describes itself as “a volunteer formation fighting on Ukraine’s side.” Little is known about the group, and it is not clear if it has any ties with the Ukrainian military. The same is true for the “Freedom of Russia” Legion.

The RVC was founded last August and reportedly consists mostly of anti-Putin Russian politicians and activists.

Meanwhile, Ukraine’s Zaporizhzhia Nuclear Power Plant, Europe’s largest atomic power station, on Monday spent hours operating on emergency diesel generators after losing its external power supply for the seventh time since Russia’s full-scale invasion of its neighbor, the head of the U.N. nuclear watchdog said.

“The nuclear safety situation at the plant (is) extremely vulnerable,” Rafael Grossi, head of the International Atomic Energy Agency, said in a tweet.

Hours later, national energy company Ukrenergo said on Telegram that it had restored the power line that feeds the plant.

But for Grossi, it was another reminder of what’s at stake at the Russian-occupied plant which has seen shelling close by.

“We must agree to protect (the) plant now; this situation cannot continue,” Grossi said, in his latest appeal for the area to be spared from the fighting between Ukrainian and Russian forces. IAEA staff are deployed at the plant, which is occupied by Russian troops.

The plant’s six nuclear reactors, which are protected by a reinforced shelter able to withstand an errant shell or rocket, have been shut down. But a disruption in the electrical supply could disable cooling systems that are essential for the reactors’ safety even when they are shut down. Emergency diesel generators, which officials say can keep the plant operational for 10 days, can be unreliable.

Grossi said it was the seventh time the plant had lost its outside power supply since Russia’s full-scale invasion in February 2022.

The Zaporizhzhia Nuclear Power Plant is one of the 10 biggest atomic power stations in the world.

Ukraine’s presidential office said Monday morning that at least three Ukrainian civilians were killed and 16 others were injured in Russian assaults over the previous 24 hours. (ap/ez)