Ukrainian troops are already putting U.S. howitzers into the fight against Russia, Defense Secretary Lloyd Austin told senators Tuesday.

During a Senate Appropriations Committee hearing on the 2023 defense budget, Sen. John Hoeven, R-N.D., asked Austin whether Ukrainian forces have the training they need to use the 90 American 155mm artillery systems the U.S. is sending to aid in the battle, especially in the eastern part of the country.

"They're using them as we speak," Austin said. "As you may know, we took a number of troops out and trained them up very quickly on 155s, put them back into action, and they are employing those weapons systems now."

A senior U.S. defense official told reporters Monday that some 200 Ukrainians have now been trained to use the M777 artillery pieces. The training was done by both U.S. and Canadian forces outside of Ukraine. Another 50 Ukrainians will begin howitzer training at an undisclosed location later this week.

The Ukrainian troops leaving the country to learn the American systems are already artillerymen, so training takes only about a week, according to U.S. officials. When they return they teach others what they learned.

Pentagon press secretary John Kirby told reporters on Monday that a "significant majority" of the 90 howitzers committed to Ukraine have arrived in country. The U.S. is also sending 184,000 artillery rounds for the weapons.

-ABC News' Matt Seyler

Civilians, including women, children and the elderly, trapped for weeks inside the Azovstal Iron and Steel Works plant in Mariupol have arrived safely in Zaporizhzhia, according to the United Nations.

A woman evacuated from the plant told ABC News in Russian, "They bombed us every day ... at night, in the morning."

"It was horrible. It is just the complete elimination of all people," she said.

"I'm relieved to confirm that the safe passage operation from Mariupol has been successful," tweeted Osnat Lubrani, the U.N.'s resident coordinator and humanitarian coordinator in Ukraine. "The people I travelled with told me heartbreaking stories of the hell they went through. I'm thinking about the people who remain trapped. We will do all we can to assist them."

Lubrani said 101 civilians were brought out of the plant and another 58 civilians from the Mariupol area joined the evacuation. The youngest was 6 months old, she said.

"It was moving and horrifying to sort of witness people that have been locked in darkness, living under incessant shelling, coming and seeing the sky for the first time in two months," Lubrani said at a Tuesday briefing.

Lubrani said some were too frightened to come out. She said they were in contact with about 30 civilians who chose not to leave, because they couldn't leave without going back into the city to find out the fate of their loved ones.

For others, Lubrani said, it was physically challenging to leave.

They had also lacked proper access to water, food and sanitation, she noted.

Many more people remain trapped at the plant. The sprawling industrial site is the last holdout for the Ukrainian resistance in Mariupol, as Russian forces accelerate their efforts to fully capture city. The Mariupol City Council has previously said there are at least 1,000 people, including Ukrainian troops, on the grounds of the Azovstal plant.

-ABC News' Zoe Magee and Christine Theodorou

Parts of Lviv are without power following missile strikes on Tuesday, Mayor Andriy Sadovyi said.

Two power substations were damaged as a result of the strikes on the western Ukrainian city, near the Polish border.

It's not clear if there are any casualties.

Ukraine's lead prosecutor, Iryna Venediktova, said Russian President Vladimir Putin should "absolutely" be prosecuted for the war crimes she says occurred in the town of Irpin and surrounding communities.

"He’s the main war criminal of the 21st century," she said.

"We all know who started this war. And this person is Vladimir Putin," she said.

Venediktova said the first phase of the war crimes investigation in Irpin has ended. She said investigators found evidence of rape, torture and the use of banned weapons of war in the city.

-ABC News' Marcus Moore

White House national security advisor Jake Sullivan hinted Thursday of more sanctions coming against Russia in the "next week or two" aimed at targeting ways Moscow is evading sanctions already imposed.

“Where our focus will be over the course of the coming days is on evasion,” Sullivan said Thursday at the Economic Club of Washington. “As Russia tries to adjust to the fact that it’s under this massive economic pressure, what steps do they take to try to evade our sanctions and how do we crack down on that? And I think we'll have some announcements in the next week or two that identify targets that are trying to facilitate that evasion both inside Russia and beyond."

When Sullivan was asked whether sanctions will automatically be lifted if a negotiated peace deal between Russia and Ukraine is worked out, he appeared cautious with his words, saying, “a lot of that depends on what the shape and scope” of the agreement is.

“A lot of it depends on what the Ukrainians, in consultation with us and the Europeans come to agree to," Sullivan said. "You know, we're not going to do a deal over the head of the Ukrainians where we give a bunch of sanctions relief to Russia. But if some measure of sanctions relief were built in to some credible diplomatic solution led by the Ukrainians, that's something that we would happily discuss."

But Sullivan said Russian oligarchs shouldn't expect to ever get back their yachts and other assets seized under sanctions that have been imposed, saying the ultimate goal is "not to give them back” once the war is over.

“The president is actively looking at how we can deal with the fact that as we seize these assets, our goal is not to give them back. Our goal is to put them to a better use than that," Sullivan said. "But I'll be careful in what I say today because there's an ongoing kind of policy process around how we end up dealing with that question. But, rest assured, that the goal is not just to sit on them for a while."

-ABC News' Justin Gomez