Ukrainian President Volodymyr Zelenskyy announced Wednesday the Security Service of Ukraine and the police arrested a suspect who they say coordinated with Russian forces in Tuesday's missile attack on Kramatorsk, a city in the Donetsk region.

The missiles struck a popular pizzeria and killed 12 people, including three children. More than 60 people were injured, the president said in a public address.

The unidentified "spotter" was charged with treason, according to Zelenskyy.

"Anyone in the world who does not understand that one cannot be an accomplice of a terrorist state must be held accountable by the entire international community," he said.

-ABC News' Will Gretsky

A senior U.S. official tells ABC News that Yevgeny Prigozhin thought he would have help from the Russian military.

Both former Russian military officers and some others in Moscow had conversations with Prigozhin before he started his march, the official said.

The U.S. doesn't believe Russian President Vladimir Putin realized this beforehand, and the officers sided with Putin in the end, the official said.

According to the official, Prigozhin was shocked he didn’t have support.

-ABC News' Martha Raddatz

Two Russian missiles struck Kramatorsk, a city in Ukraine's Donetsk region, killing at least four people, according to officials.

At least 47 people were injured in the attack, but the death and injury toll could rise.

One of the deceased victims was a 15-year-old and one of the wounded victims was a child under a year-old, officials said.

One missile struck an eatery downtown and the other one hit the outskirts of the city, Andriy Yermak the head of the Ukrainian Presidential Office said.

A restaurant and a hotel were badly damaged as a result of the strikes, according to officials.

Crews continued to dig through the rubble to search for victims throughout the evening.

"Each such manifestation of terror proves over and over again to us and to the whole world that Russia deserves only one thing as a result of everything it has done - defeat and a tribunal, fair and legal trials against all Russian murderers and terrorists," Ukrainian President Volodymyr Zelenskyy said in a statement.

-ABC News' Fidel Pavlenko and Ellie Kaufman

The U.S. announced additional sanctions targeting the Wagner Group, specifically going after gold companies and a Russian man it says are illicitly funding the Wagner Group’s operations in Ukraine and Africa.

Central African Republic based companies Midas Resources SARLU and Diamville SAU, Dubai based company Industrial Resources General Trading and Russia based company Limited Liability Company, re connected to Wagner’s leader Yevgeny Prigozhin, who is already subject to U.S. sanctions along with numerous other entities linked to the Wagner Group, according to the Department of the Treasury’s Office of Foreign Assets Control.

Andrey Nikolayevich Ivanov, a Russian national, and an executive in the Wagner Group, allegedly worked closely with Prigozhin’s entity Africa Politology and senior Malian government officials on weapons deals, mining concerns, and other Wagner Group activities in Mali, OFAC said.

"The Wagner Group funds its brutal operations in part by exploiting natural resources in countries like the Central African Republic and Mali," Brian Nelson, the U.S. under secretary of the treasury for terrorism and financial intelligence, said in a written statement. "The United States will continue to target the Wagner Group’s revenue streams to degrade its expansion and violence in Africa, Ukraine, and anywhere else."

-ABC News' Ben Gittleson

In the wake of Saturday's short-lived attempted rebellion against the Kremlin by the Wagner private military company, Mikhail Khodorkovsky, an exiled oligarch considered one of Putin’s best-known opponents, told ABC News he supports the mutiny and encourages Russians to back the leader of the mercenary group.

Once Russia’s richest man, Khodorkovsky, a Putin opposition activist, spent 10 years imprisoned after he challenged Putin, his case now considered a foundational moment for Putin’s regime.

When Wagner founder Yevgeny Prigozhin and his fighters marched on Moscow Saturday before making a sudden about-face, Khodorkovsky was notable among Russia’s pro-democracy opposition in calling on people to support Prigozhin, arguing that allowing him to remove Putin would create an opportunity for the democrats.

Khodorkovsky told ABC News he believed Prigozhin’s actions were a real coup attempt and that it had “seriously undermined” Putin’s power. He predicted that similar opportunities to collapse the regime will be launched soon.

"The blow to Putin’s reputation, to the authorities’ reputation, was absolutely fantastical," Khodorkovsky said. "Putin’s government today is, without a doubt, strongly undermined by what happened -- his authority, his ability to control the security services is seriously undermined."

Khodorkovsky said Prigozhin’s march on Moscow had undermined Putin’s popularity, showing neither ordinary Russians nor the security services were prepared to act to protect him.

“Along the entire route of Wagner's columns, no one in any way tried to hinder him (Prigozhin). Even the security forces did not try to stop him," Khodorkovsky said. “It showed that, in fact, inside the country, Putin has an absolute void."

Khodorkovsky said he did not support Prigozhin himself -- considering him a "war criminal" -- but that the democratic opposition should have sought to help him overthrow Putin, and then taken power from him after.

Khodorkovsky criticized other parts of the anti-Kremlin opposition who attacked him for calling on people to assist Prigozhin, saying he believed the opposition had “slept through” the opportunity and suggesting it should have sought to stage a rebellion in Moscow at the same time.

"There will definitely now be more such opportunities because of Putin’s weakening. But the next time we need to simply be more ready," said Khodorkovsky, who is living in exile in England. "If an uprising had started in Moscow to meet Prigozhin then a situation could have developed quite differently.

ABC News' Patrick Reevell