'Back in May, the Biden administration started giving Ukraine the green light to strike over the border into Russia using U.S. weapons, provided it was for self-defense. Now, this was a big deal because previously it was only allowed to use those weapons in areas within Ukraine that Russia had already occupied.

An angry Putin saying NATO risks a full on war with Russia, but that Moscow might also give arms to U.S. adversaries around the world.

'Ukrainian soldiers told CNN they noticed the difference that those strikes slowed the Russians down before they even crossed into Ukraine. However, it's one thing to send rockets into Russia, but a full on ground incursion. That option didn't seem to be on the table. Well, until recently, that is. My guest is Daria Tarasova-Markina. She's a Ukrainian journalist who has been working hand in hand with our CNN teams on the ground. We spoke on Thursday. Today, the story of how a surprise dash across the border caught the Russians off guard, and how it could change the course of the entire war. From CNN, this is One Thing. I'm David Rind.

So, Daria, where are you right now?

So right now, north of Ukraine, it's summer region. Because right now it's probably for sure, you know, that course commission is going on. I'm here with a CNN team covering this story. This is not far away from Russian border where this story's going on right now.

Right. The Kursk region. This is where this whole incursion is happening. But can you tell me how did it start?

So, yeah, it's very interesting story. Everything started on August 6th. The West. Something sounds had happened. We saw some statements from Russian security sources. They said that it was some provocation on the border, like, okay, it's not the first time, you know, provocation on the border. Then we found that some kind of statement from the Russian Amadeu, minister of defense.

According to Russian officials, this is indeed the Ukrainian regular military, launching now for two days and incursion across the border into Russia, near a town called Suzhjan.

Now and then there were more and more and more information. But Ukraine said nothing like nothing from authorities.

And then we started seeing videos from soldiers who were coming to the territory, and there were a big number of Ukrainian troops on the Russian territory.

Ukrainian troops appeared to have captured an important natural gas hub in Russia's Kursk region. Video of them standing in front of the facility was posted on unofficial telegram channels. CNN has geolocated this footage from the Kursk region, which shows burnt out Russian military trucks and the bodies of military personnel.

And you started calling authorities, Ukrainian authorities asking what's going on? And no one said nothing like just it was silence. And then there were more and more and more and more video on social media. And yeah, we understood that. Okay, this is serious.

Ukrainian troops sweeping through Russian territory...Dear Ukrainians, this soldier starts and then says his forces went into a Russian supermarket, but that Ukrainian stores have a better selection. Ukraine? Yeah. Haha.

And eventually in a few days, Ukrainian authorities said that. Yes, this is the mission. Yeah. Keep going. We are coming there and we are just taking one village at the second village. And you saw all of these Russian prisoners that were taken as P.O.W. so we saw all of the bottles. And now we are here. It's more than one week. And now there are like more than 70 settlements.

I think President Zelensky says in the last 24 hours, Ukrainian forces have seized another 15mi2 of Russian land in the Kherson region. That brings the total of the weeklong surprise incursion to nearly 400mi2. And to put that into perspective, that's as much ground as Russia has gained in Ukraine over the last year.

And can you put into perspective just how big a deal it is for the Ukrainians to go across the border like they did because like they had been firing rockets, but this was actually going to take villages, right?

Yeah, exactly. I mean, we have troops on the ground. There are Ukrainian soldiers who are already in that territory. It's not just sent in drones or missiles. It's just like taking P.O.W.. So it's coming to this abandoned to Russian positions.

Now, this is what's so startling about this offensive, the volume of Western supplied armor that we're seeing passing back and forth.

So today we're very near the border. The border itself is destroyed. We were on on Ukrainian side, so we did not cross the border yet. But still, just to see this huge destructions everywhere, to see this Russian signs on the border that was destroyed.

It's also remarkable the freedom with which the Ukrainian military is moving around here. They simply aren't afraid of the drones that have hampered their every move for the past months.

And we saw a lot of vehicles that were going in, going out and Ukrainian soldiers that were there, and they seemed quite relaxed. You know, they were just like you didn't feel that. It was like very nervous, very active.

Seem like they were in control of the situation.

Yes, yes, yes, exactly. Yeah. You're totally right.

You have families individually, which, if you're not in there.

We are in touch with several, like, soldiers who are already there. And they are doing this mission. They are moving forward. No one knows. Like the final strategy. No one talks about the final goal. And we asked authorities. We asked just ordinary soldiers. Just today the soldier told us, I'm just doing my task. I have to and I'm doing it right now. So it seems that no one talks about the strategy. No one talks about it. Where are you going? Like, what's the final goal of this?

Right? I mean, that's what I was going to ask, like, how far do they want to go? Is this just to punch Russia in the nose, or is there some greater objective at play here?

It's quite difficult to say, you know, because probably only Ukrainian authorities and military generals know it. It could be probably to do a buffer zone to protect Sumy because, I visited yesterday, the shelter where the people are coming from, regions that are very, very close to the border. And those people told me that previously Russian soldiers used artillery. Now they can't do it because they were moved.

So because Ukraine has moved past the border into Russia, there's like a zone. Yes. And Russia can't, you know, fire right into these villages right along the border. You're saying.

Exactly. Yeah. This is what these residents told me. But now, Russian soldiers, they're using cops. This is aerial guided bombs, which is hugely devastating. But still, it's not so many artillery. There are not so many drones. So it could be the one reason. The other one reason. Maybe. Maybe this is something for the morale. Because I can tell you that the morale in one soldiers is super high.

How does it feel to be in Pushchina?

Dreams come true.

One commander with whom I talked to yesterday, he told me, that dreams come true. He meant that we have been fighting here. I mean, they have been fighting here in Ukraine for years. And his message was, if Russian came to a Ukrainian, a land to fight. So that means that this war can come back to their land. He told me they, talk via talk, you know. Yeah. So. And for them, they morale is, like, just super high. You can feel it in the air.

Well. So how has Russia been dealing with this? Because they seem to have been totally caught off guard by this.

Yeah. So you could see there too, there are a lot of P.O.W.. So these they are soldiers. They just they are not fighting. And again, that commander whom I talked to yesterday, he told me, it's so interesting. It seems that Russian soldiers, they are ready to die for Ukrainian land, but they are not ready to die, for they own the land.

So I guess.

The Russians are now trying to stop our advance. They have pulled in reserves, which has benefited our defense forces in other areas because it's become easier to work there. We have information.

From what I was told to also by the same military guys that Russia trying to protect their land. They move their soldiers from Crimea, from Zaporizhzhia, from like Kharkiv direction, and they see that Russian are moving their troops from different direction.

So they're diverting troops from Ukraine into Russia to go deal with this.

Yeah, of course they have to. I mean, they have to do something. Yeah. And they need people for this. So, yeah, they just move their troops from other battlefields.

What is the reaction been from the U.S. and the international community? Because it is honestly kind of reminiscent of what Russia did to them two years ago. Obviously that was completely unprovoked on the part of Russia. But are there any concerns about an escalation like this?

'Well, of course you have seen that the statements were quite accurate here, that most countries supported Ukraine's right to self-defense. Again, Ukrainian authorities are very careful with the statements. But again, coming back, we talked about morale among soldiers. You know what I was surprised to see in this, evacuation center here in Ukraine. Normally when you come to such places, you will feel a high level of desperation, because people had to leave their houses. They don't know whether they can come back to their place and so on.

Kateryna Mykolaevna, you left today, right? You are very close to the border.

Well, there are not even five kilometers

Here in Sumy region when it came to this evacuation center.

A new live show which. Stood near.

I found that people were scary, obviously, but still they supported Ukrainian army and this level of hope. You could feel it.

Do you hope to return soon?

I hope it will end soon and I will be home. See, everything

I mean, it was it was higher than the level of fear. And it was interesting. So maybe they saw one of the targets, one of the goals, I mean, I, I don't know, let's see.

You're a native Ukrainian, right. Like this. This is your home.

Yeah. Yeah.

So what has it been like reporting on this war for the last two plus years?

You know, I was thinking who I am, I am I generally, so I am a Ukrainian. But, no, obviously, of course it's it's difficult because you're trying every time you're trying to stay objective, you are trying not to to be too emotional. You're just trying to tell the facts. But at the very end of the day, of course, it's your country. It's your people. You have more feelings than just covering the story. But one CNN producer once gave me a very good advice. He told me, hey, listen, bed is bed good is good. So when you are on the ground, just think about it, not about who you are. Where are you from? Just when you're telling stories, try to understand whether it's good or bad. So yeah, I'm just trying to tell the stories, trying to show, to show what's going on here, trying to show people stories. Because at the very end of the day, I think that story really matters, that this is something that connects all of us all around the world. And just to help people who live in very, very far away to understand what's going on here or there. Yeah, of course, it's difficult to cover the war when there's the war in your country. But yeah, we try to do our best.

Well, thank you so much for bringing us these stories. Really appreciate it there. Thank you.

Thank you. Thank you. David.

One thing is a production of CNN Audio. This episode was produced by Paola Ortiz and me, David Rind. Our senior producers are Felicia Patinkin and Faiz Jamil. Matt Dempsey is our production manager. Dan Dzula is our technical director, and Steve Lickteig is the executive producer of CNN Audio. We get support from Haley Thomas, Alex Mansory, Robert Mathers, John Dianora, Leni Steinhart, Jamus Andrest, Nichole Pesaru, and Lisa Namerow. Special thanks to Gul Tuysuz, Victoria Butenko, Ivana Kottasová, Wendy Brundage and Katie Hinman. We'll be back on Wednesday with an episode from the Democratic National Convention in Chicago. Big political week ahead. So head over to CNN.com or the CNN 5 Things podcast for all the updates. In the meantime. I'll talk to you later.