AMNA NAWAZ: This week, Ukraine's government launched its most aggressive anti-corruption efforts since Russia's invasion.

A well-known billionaire and six former Defense Ministry officials are among dozens of officials targeted, some accused of embezzlement.

That internal battle comes as the front line with Russia heats up.

Today in Eastern Ukraine, Russian missiles hit homes and a children's clinic, just the latest sign Russia targets civilians indiscriminately.

Nick Schifrin speaks to the man whose office is trying to ensure accountability for both corruption and war crimes.

NICK SCHIFRIN: This is all that remains of what used to be apartments, all that's left of a kitchen, the pulverized ruins left over from a Russian missile that landed overnight, the ripped-open insides of multiple living rooms, bedrooms, families' lives, their contents now a single collection.

Ukrainians are already cleaning up after Russia's latest missile strike.

The accountability is just beginning.

We spoke to Ukraine's prosecutor general, Andriy Kostin.

ANDRIY KOSTIN, Prosecutor General of Ukraine: Their massive missile attacks which are happening every week or every two weeks cause death of dozens of civilians.

NICK SCHIFRIN: Kostin visited Washington, D.C., this week to rally support in his pursuit of justice.

He says multiple Russian recent missile strikes, last month in Dnipro, that ripped in apartment building in two, last summer in Kremenchuk took that gutted a mall were conducted with the same type of Russian missile by the same Russian unit that he wants to prosecute.

ANDRIY KOSTIN: We definitely know that this type of missiles is only within the one squad of Russian air forces.

So, of course, this work is very difficult and it takes a lot of time.

But our aim is to find everyone who is responsible for committing such atrocious war crimes on Ukrainian land.

And we will go ahead with this.

NICK SCHIFRIN: The International Criminal Court would not be able to pursue Russia's most senior leadership for the crime of aggression.

So, Ukraine wants to create a special tribunal, an idea supported by the European Union and United Kingdom, but not the U.S. ANDRIY KOSTIN: I'm optimistic.

And I hope, in coming days or weeks, we will have a political decision of U.S. government to support the ad hoc special tribunal for the crime of aggression.

I believe final decision will be to support the special tribunal, because crime of aggression is a -- was a primary war crime.

If aggression would not occur, there would be no these 65,000 war crimes committed, no people killed, tortured, raped, or illegally displaced.

And one of the initiatives of Ukraine is also to use all the procedures of the International Criminal Court within the special tribunal to make it credible also from the criminal procedural point of view.

NICK SCHIFRIN: The Americans and even the Europeans in the last few days have talked about an interim prosecutor in The Hague to gather evidence of the crime of aggression that is separate from a special tribunal, though.

Is that good enough?

ANDRIY KOSTIN: It's very good idea.

This office will combine Ukrainian prosecutors and prosecutors from other jurisdictions, which will select evidences for the case of the crime of aggression for the future tribunal.

NICK SCHIFRIN: Simultaneously, Kostin vows to fight an internal war against corruption.

This week, the equivalent of FBI agents accused the head of Kyiv's tax service of embezzling millions and living well beyond her means.

Agents raided the home of one of Ukraine's richest and most famous men, Ihor Kolomoisky, connected to companies accused of massive tax evasion.

Last week, one of Zelenskyy's deputy chiefs of staff posted his own resignation letter after he was forced out.

And now half-a-dozen defense officials are accused of buying low quality protective gear for Ukrainian soldiers at inflated prices.

ANDRIY KOSTIN: We have informed on suspicion several top officials of Ministry of Defense, of regional administrations, of Ministry of Energy.

It's a signal from me and from my colleagues for everyone, including oligarchs, including former officials and current officials, that there will be no tolerance for corruption.

And this is strong position of president of Ukraine.

VOLODYMYR ZELENSKYY, Ukrainian President (through translator): Unfortunately, in some spheres, the only way to guarantee legitimacy is to change leaders, change as many as necessary to ensure people do not abuse power.

ANDRIY KOSTIN: And this is a strong position of all Ukrainian nation, because we build new European Ukraine without corruption.

We have wartime priorities, but corruption is an internal enemy of Ukraine, and should be defeated together with external enemy Russia.

NICK SCHIFRIN: You call it a signal for current and future actors.

But is it also evidence that Ukraine is still bedeviled by the corruption that has existed for many years?

ANDRIY KOSTIN: The most important thing is to react, because the reaction on cases in -- on time and reaction on cases will stop future potential officials from corruption activity.

And this is our goal, to have our country cleaned from corruption.

NICK SCHIFRIN: And does that include your own office?

You have fired one of your deputies.

Is that a case of corruption or perhaps vacationing in Europe when he wasn't supposed to?

ANDRIY KOSTIN: In some times, people make mistakes.

And if they understand that these mistakes are substantial, they can leave their position.

I also fired five regional prosecutors the next day.

And this is not the end.

We will go ahead, because we all need the efficient state institutions and efficient state structures.

And we have no time to wait until someone can fix mistakes which occurred.

And I'm grateful.

I'm grateful today for every investigator, every prosecutor doing their work in this very difficult situation, because, sometimes, we are without electricity, sometimes without connection.

But there was no day in Ukrainian history since 24th of February when Ukrainian authorities were not active.

All authorities work every day, including law enforcement.

And this will be proceeded.

NICK SCHIFRIN: Andriy Kostin, Ukraine's prosecutor general, thank you very much.

ANDRIY KOSTIN: Thank you.