How Ukraine struck a major blow to Russian forces

Ukrainian troops made good on President Volodymyr Zelenskyy's call to take back lands claimed by Russian forces with an aggressive counteroffensive this weekend in the country's northeast region.

Ukrainian officials said they drove out Russian forces in two key areas in the Kharkiv region.

And Ukrainian officials said they are not going to let up.

ABC News' Tom Soufi Burridge, who is in Kiev, spoke with "Start Here" about this major turning point in the war with Russia and how it came about.

TOM SOUFI BURRIDGE: This is a breathtaking move by the Ukrainians. So, people might have heard about the counteroffensive in recent days. We've been talking about it a lot in relation to the south of Ukraine. In the early days of the war, Russia occupied a large amount of territory down in the South, north of the Crimean Peninsula. Now, the Ukrainians started pushing a few weeks ago. So, they were taking a few villages, nothing much. It was moving slowly. There was a bit of a media blackout. And then suddenly, in the middle of this week, we got a huge breakthrough from the Ukrainians and actually it was in the northeast.

It seems that they were kind of distracting the Russians in the south, pulling their attention there, and then they hit the Russians hard in the northeast and really seemed to have caught them completely off guard. I mean, we're seeing videos online of abandoned Russian tanks in these cities and villages that the Ukrainians have taken as if the Russians have basically fled in a hurry. And the Ukrainians, it's really got to be stated that up in the northeast, not far from the second largest city called Kharkiv. The Ukrainians have smashed through and taken massive amounts of territory, dozens of villages, [and] at least three cities, a key strategic city among them. And the Ukrainians [are] saying it's tantamount to about a thousand square miles of territory. Unbelievable.

START HERE: The first question that comes to mind is how is that possible?

TOM SOUFI BURRIDGE: Well, one of the, one of the reasons is the U.S. supplied weapons and weapons from other allied nations. That's definitely turned the tide in this war.

For weeks, if not months, you know, those weapons -- and we're talking about the heavy weaponry, rocket systems -- to hit targets behind the Russian lines, ammunition depots, command and control centers that are used to run the Russian war machine. That's been happening for a while now. We've seen the evidence. We've seen the Ukrainians hitting all those targets and key infrastructure to block off the Russian supply lines so they can't get supplies so easily into their troops in certain areas, particularly around rivers. And that's been done very effectively by the Ukrainians. Exactly how they sort of punch through the lines in this particular area, we just don't know at this stage.

The Ukrainians have put out a sort of quite effective media. Blackouts may be the wrong word, but it's a kind of shutdown on any access to the front lines. They really haven't been letting journalists in. The amount of information we've been getting out is sort of slow and therefore we're sort of still trying to build a picture of exactly how they did this. But it's remarkable. I think it speaks of the confidence of the Ukrainians, [and] the morale of the Ukrainians. I think it also speaks of how Russian forces are overstretched.

U.S. intelligence has been telling us that for a while now. This is evidence of that, but I think it really shows how the Ukrainians seem to have the momentum clearly, and they're going forward now.

START HERE: Because there's not a great way to verify a lot of this, Russia has actually said not all these are hasty retreats. They have admitted they're retreating from some of these positions, but some, they say, are sort of planned consolidations the way they said with their original retreats. Overall, though, Tom, can you just help me get a sense, then, of where the Ukrainian military is going from here? What will their endgame be? Because Zelenskyy says he wants it all back.

BURRIDGE: Right now, the Ukrainians are pushing to retake the whole of the Kharkiv region in the northeast. That'll be hugely significant. Again, a massive blow to Putin and the Kremlin. Beyond that, politically, they want to recapture all of their land. They're way off doing that. So we can't get carried away with ourselves. This is Russia. We're talking about -- a massive military machine. But we're already seeing the Russian response: retaliation hitting power lines, hitting power stations, causing massive blackouts across the country. It's worth just sort of adding in here that Zaporizhzhia nuclear power plant, we've all heard about it, the concerns there.

Again, [there were] alarming developments over the weekend, more shelling in the area. So, basically, the plant lost all of its external power supply and momentarily they had to shut the last remaining reactor down. Since then, they have actually regained the external power line. But the UN's nuclear watchdog warning this weekend quite clearly that if the shelling doesn't stop the possibility of a nuclear accident there is very real.

Going forward, it remains to be seen whether Ukrainians can consolidate these gains, take even more territory or whether Russia is going to find a way to hit back.

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