AMNA NAWAZ: The Russian mercenary leader Yevgeny Prigozhin is said to be under investigation by Russian intelligence tonight, after claiming that Russia's war with Ukraine was started under false pretenses by top military officials.

Prigozhin has thousands of personnel aiding Russia's onslaught in Ukraine, and he now says Russian troops have fired on his forces.

There also reports riot police and the National Guard are tightening security at government buildings in Moscow tonight.

Meantime, as Lindsey Hilsum of Independent Television News tells us, Ukraine's capital, Kyiv, has sprung back to life under the watchful eyes of air defense crews that guard the city.

LINDSEY HILSUM: Every night over Kyiv and other cities, air defenses protect Ukrainian civilians.

Every morning, in an undisclosed location just outside the capital, the radar, guns and controls of a German Gepard system are prepared for action.

Each gun fires 550 rounds per minute.

In the last six months, this crew has shot down four Iranian-made Shahed drones and two cruise missiles, preventing death and destruction in the city.

ROMAN, Crew Commander (through translator): The main advantage of this self-propelled anti-aircraft gun is that it's simple to use, because of the computer system and ease of control.

Another important thing is that relatively cheap shells can be used to shoot down the very expensive significant targets that our enemy has.

LINDSEY HILSUM: The Ukrainian military celebrated the arrival of two Patriot batteries from the U.S. and Germany in April.

These missiles, by contrast, cost $4 million to fire, but they can shoot down ballistic and hypersonic missiles at long range.

Last March, we saw the impact of a rocket strike on an apartment block in Kyiv.

The mayor of the capital, Vitali Klitschko, was there, and Olha Timoschuk from a neighboring block.

OLHA TIMOSCHUK, Kyiv Resident: It is 50/50.

Either you get hit or not.

LINDSEY HILSUM: Now the block has been rebuilt, better than before, complete with phoenix mural.

But Olha no longer thinks she might have to leave the city.

OLHA TIMOSCHUK: I sleep better at night, to be honest.

Sometimes, I don't even hear the sirens.

So, I go to sleep and I know that I will wake up in the morning, actually.

I believe in that more than I did last year, to be honest.

And now it's -- it's, like, easier, yes.

Feels better.

LINDSEY HILSUM: And what do you feel about the guys who are manning the air defenses?

OLHA TIMOSCHUK: Oh, they're heroes.

(LAUGHTER) LINDSEY HILSUM: But last month saw an onslaught.

And while 154 missiles were shot down, 18 got through, killing five people.

The mayor of Kyiv is, therefore, more circumspect.

VITALI KLITSCHKO, Mayor of Kyiv, Ukraine: Yes, of course.

Blue sky, great weather, summer, it's peaceful atmosphere, and but it's illusion.

LINDSEY HILSUM: It's an illusion?

VITALI KLITSCHKO: It's illusion.

It's, any moment, we can listen air alarm, bombing alarm.

It mean that every moment the -- every building can be destroyed from Russian missiles.

LINDSEY HILSUM: Kyiv is full of outdoor cafes and bars.

After the Russians were pushed back from the outskirts last spring, many people reverted to their old life, deciding that the odds of being hit by a missile or drone were acceptably small.

Sometimes, it's hard to remember this is a city at war.

The contrast with the destruction and relentless fighting in the east is stark.

The air defense crews prepare for another night.

The safety of the capital's civilians is in their hands.