At least 21 people were killed and 48 injured by shelling in the Kherson region on Wednesday, Ukrainian officials said, as the death toll continues to rise.

A railway station and market in the city of Kherson were hit in strikes, which occurred across the Kherson region in southern Ukraine, officials said.

"A railway station and a crossing, a house, a hardware store, a grocery supermarket, a gas station -- do you know what unites these places? The bloody trail that [Russia] leaves with its shells, killing civilians in Kherson and Kherson region," Ukrainian President Volodymyr Zelenskyy said on Twitter.

All the victims were civilians, Zelenskyy said.

An ambulance was also damaged in the strikes, according to Ukrainian Prosecutor General Andriy Kostin.

"No military objects here. Just civilians, including children," Kostin said on Twitter.

At least one person was killed and three injured in the strike on the railway station, officials previously said.

The Biden administration has announced a new $300 million military aid package for Ukraine.

The package includes additional ammunition for U.S.-provided High Mobility Artillery Rocket Systems, as well as "additional howitzers, artillery and mortar rounds, and anti-armor capabilities that Ukraine is using to push back against Russia’s unprovoked war of aggression," the Department of Defense said in a statement.

This marks the Biden administration’s 37th drawdown of equipment from Defense Department inventories for Ukraine since August 2021.

Ukrainian President Volodymyr Zelenskyy rejected Russia's claim that his country was involved in the drone attack on the Kremlin early Wednesday.

Zelenskyy, who is currently in Finland, said the claim was the prelude to a "large-scale terrorist attack" from Russia.

"First of all, Ukraine wages an exclusively defensive war and does not attack targets on the territory of the Russian Federation," Zelenskyy said in a statement. "What for? This does not solve any military issue. But it gives RF grounds to justify its attacks on civilians."

Zelenskyy went on to say that various attacks in Russia could be the result of "guerrilla activities of local resistance forces."

Russian President Vladimir Putin's spokesman has accused Ukraine of trying to strike Putin's residence in the Kremlin with two drones overnight, but said they were brought down before they could reach their target.

No injuries were reported, Kremlin officials said. Putin was not at the residence at the time, they said.

Videos released on official social media channels appeared to show a drone strike the roof of the Senate Palace at the Kremlin.

The Kremlin said that "the Russian side reserves the right to retaliate whenever and wherever it deems necessary."

-ABC News' Patrick Reevell and Tanya Stukalova

Russia's security services have arrested an anti-Kremlin political commentator who the jailed Wall Street Journal reporter Evan Gershkovich met with shortly before his own arrest.

Yaroslav Shirshikov has said he spent two days showing Gershkovich around the city of Yekaterinburg during a reporting trip there a couple of weeks before Russia seized Gershovich.

Shirshikov said he had been due to meet with Gershkovich again the week the reporter was arrested in the city.

This morning, local media published video showing masked security officers detaining Shirshikov in his apartment and searching it.

A local news outlet cited a security services representative saying Shirshikov may have been arrested for posting comments cheering the assassinations of two ultra-nationalist pro-war figures, Daria Dugina and the blogger Vladen Tatarsky.

The site UralLive quoted a law enforcement source that Shirshikov was detained on a charge of “justifying terrorism”, which carries a maximum sentence of 7 years prison. It linked the charge to a social media post in which Shirshikov wrote he wasn’t sad over the death of Tatarsky, who was killed in a bomb attack in St. Petersburg this month.

Shirshikov spoke to several international media outlets including ABC following Gershkovich's arrest. He said that Gershkovich had acted entirely as a professional journalist in Yekaterinburg, conducting interviews openly and doing usual reporting.

Shirshikov is a critic of the Russian government and has spoken publicly about his opposition to the war in Ukraine.

-ABC News' Patrick Reevell