According to independent observers, Ukrainian units have broken through several front sections and advanced far into previously Russian-occupied territory.

The Reuters emissary, one of the few journalists on the ground, reports on how Ukrainian police are now patrolling the villages given up by fleeing Russians.

Pictures posted on social media by Natalia Popova, adviser to the Kharkiv regional government, show Ukrainian soldiers raising the country's flag in Kupiansk, an important junction for the railway from Russia.

"Kupiansk is Ukraine.

Glory to the Armed Forces of Ukraine," reads the text.

Later on Saturday, Ukraine's security service SBU also announced that the city had been recaptured – the first official confirmation of the counter-offensive.

The British Ministry of Defense assesses that the Russian military leadership was not prepared for the counterattack, and that the sector was only lightly defended.

Moves towards Izium

And the offensive is going faster than most expected.

According to the ISW think tank, in the last 24 hours, Ukraine has recaptured 1,000 square kilometers of previously occupied areas in Kharkiv County.

The focus now appears to be on Izium, an important hub for the transport of weapons and ammunition to the Russian occupation forces.

According to information on Saturday, the city is surrounded and is being attacked from several directions.

The data is difficult to verify because Ukraine does not allow independent journalists to cover the counteroffensive.

But the successes are also confirmed by the Russian side:

- Attempts are being made to remove the Ukrainian forces, but there are fierce battles and our troops are pushed back when they advance, says the Russian-appointed official Vitaly Gatyev in a televised speech.

"Outsmarted us"

While Russian media show convoys of vehicles allegedly on their way to reinforce the Kharkiv region, more and more pro-Russian military observers are openly airing their displeasure with the war efforts.

Not least as Ukraine is currently having success on two fronts: Kharkiv in the north and Kherson in the south.

"We have to be honest, the Ukrainian leadership has outsmarted us here," writes the pro-Russian Ukrainian blogger Jury Podoljaka, with an audience of one million on Telegram, according to The New York Times.

According to Katarina Engberg, senior adviser at Sieps, however, one should be careful about making big assumptions about what the Ukrainian successes on the battlefield mean in the longer term.

- Ukraine has gained a marginal advantage right now, but that should not be confused with any strategic decision for the outcome of the war.

What it's about is moving your positions forward so that you can strengthen before the winter, she says in SVT's Morgonstudion.