At least two people were killed and 19 others injured from a Russian drone attack in northern Ukraine, the Sumy Regional Military Administration said.

An administrative building and two apartment buildings were damaged in the four drone strikes, officials said.

Four people have been hospitalized, according to officials. Two of the patients were listed in intensive care.

Ukrainian President Volodymyr Zelenskyy said in his daily evening address that the lack of air defense systems is part of the reason buildings were hit.

"The enemy is taking advantage of this," he said.

-ABC News' Ellie Kaufman

Lynne Tracy, the U.S. ambassador to Moscow, met with detained American journalist Evan Gershkovich on Monday, the ambassador's press secretary told ABC News.

Tracy met with Wall Street Journal reporter at Moscow's Lefortovo prison where he's being held, according to the press secretary.

This is the second visit between Tracy and Gershkovich since his initial detention in March.

-ABC News' Tanya Stukalova and Ellie Kaufman

Yevgeny Prigozhin, the Wagner Group leader who led the rebellion in Russia, reportedly released a new message Monday, his first in a week, to a social media account with ties to the PMC.

In a short audio message posted by Grey Zone telegram account, which believed to be run by a Wagner member that frequently posts about events on the frontline in Ukraine, Prigozhin claimed the June 24 rebellion against Moscow was aimed at "fighting traitors and mobilizing our society."

"I think we have achieved a lot of it. In the near future, I am sure that you will see our next victories at the front. Thanks guys," he allegedly said.

The Wagner Group leader said "today, more an ever, we need your support."

-ABC News' Patrick Reevell

Amid fears Russia might blow up the Zaporizhzhia nuclear power plant, Ukraine is holding drills to prepare emergency services with how to deal with a potential radioactive disaster.

ABC News was invited to the drills in the city of Zaporizhzhia this week, about 30 miles from the plant, where firefighters in hazmat gear simulated decontaminating people from radiation during an evacuation.

Emergency workers demonstrated scanning civilians with Geiger counters as they disembarked buses, stripping some civilians and hosing them with water as they lay on stretchers. Firefighters in yellow suits sprayed down vehicles and moved them through a large washer system rigged up between fire trucks.

This week, Ukraine's chief of military intelligence, Kyrylo Budanov, claimed Russia had now completed preparation to potentially sabotage the plant if it chooses.

Read more about the drills here.

-ABC News' Patrick Reevell

Gen. Mark Milley, the U.S. military's top general, told reporters Friday that it's likely too early to tell the impact of the Wagner Group mutiny on Russian President Vladimir Putin.

"We want to know the answer to that question," Milley said when asked at the National Press Club if Yevgeny Prigozhin's mutiny had left Putin weakened. "I don't think we have evidence, conclusive evidence, either way, yet too early to tell."

Milley acknowledged that Ukraine's counteroffensive is making steady progress, but moving slowly -- something he said was not surprising given how tough of a fight it is.

"At the end of the day, Ukrainian soldiers are assaulting through minefields and in the trenches, and this is literally a fight for their life. So yes, sure, it goes a little slow, but that is part of the nature of war," Milley said.

He also noted that the U.S. is considering sending cluster munitions to Ukraine, though no decision has been made.

-ABC News' Luis Martinez