The death toll from a Russian rocket attack as Ukraine observed its Independence Day has risen to 25, including an 11-year-old boy found under the rubble of a house and a 6-year-old killed in a car fire near a train station that was the target, a Ukrainian official said Thursday.

Russia's Defense Ministry said its forces used an Iskander missile to strike a military train that was carrying Ukrainian troops and equipment to the front line in eastern Ukraine. The ministry claimed more than 200 reservists "were destroyed on their way to the combat zone."

The deputy head of the Ukrainian presidential office, Kyrylo Tymoshenko, did not say if the 25 victims he reported from Wednesday's attack all were civilians. A total of 31 people sustained injuries, he said.

The lethal strike in Chaplyne, a town of about 3,500 residents in the central Dnipropetrovsk region. nonetheless served as a brutally painful reminder that Russia's military force is causing civilians to suffer and testing Ukraine's resilience after six months of a grinding war.

In Geneva on Thursday, the U.N.'s human rights chief, Michelle Bachelet, decried the time since Russian President Vladimir Putin sent troops into the neighboring country as "unimaginably horrifying." She called on Putin "to halt armed attacks against Ukraine."

The train station strike took place after Ukrainian President Volodymyr Zelensky warned that Moscow might attempt "something particularly cruel" this week as Ukraine marked both its 1991 declaration of independence from the Soviet Union and the six-month point of Russia's invasion on Wednesday.

Tetyana Kvitnytska, deputy head of the Dnipropetrovsk regional health department, said the people wounded in the attack suffered a range of injuries.

"There are craniocerebral injuries, limb fractures, many patients with explosive and shrapnel injuries, burns," she said. "People were in a difficult condition, both physically and psychologically."

"Now our efforts are focused on the children who suffered. We work with four children. Three children out of four are in serious condition. In addition to severe stress, they have blast and shrapnel injuries, burns, and fractures," Kvitnytska said. "The children are in serious condition."

The Russian government has repeatedly claimed following attacks in which civilians died that its forces only aimed at legitimate military targets. Hours before the train station attack, Russia insisted it was doing its best to spare civilians, even at a cost of slowing down its offensive in Ukraine.

Russian Defense Minister Sergei Shoigu, speaking Wednesday at a meeting of his counterparts from a security organization dominated by Russia and China, said Russia was carrying out strikes with precision weapons against Ukrainian military targets, and "everything is done to avoid civilian casualties."

"Undoubtedly, it slows down the pace of the offensive, but we do it deliberately," he said.

It was the second time Shoigu has made such a claim; he said the same thing in late May.

Elsewhere in Ukraine, three people were killed in the eastern region of Donetsk on Wednesday and one more was wounded, Gov. Pavlo Kyrylenko said on Telegram.

Nikopol, a city across the river from the Zaporizhzhia Nuclear Power Plant, came under more Russian shelling overnight, Valentyn Reznichenko, the governor of the Dnipropetrovsk region, said.