A Ukrainian counteroffensive appears to be progressing in the north, but less so in the southern Kherson region that has attracted greater attention and Russian reinforcements.

Ukrainian officials and Russian military bloggers alike on Thursday described a counteroffensive in the north that has surprised in its speed, the first time since the war began that Ukrainian forces have been able to push past Russian defenses on a more than tactical level.

The limited breakthrough comes as Russia's President Vladimir Putin ratchets up pressure on European energy markets. That has officials in Kyiv racing to show allies the war can be won.

In the few days since the offensive began with an assault on the town of Balakliya, about 90 km (56 miles) south east of Kharkiv, Ukraine's second largest city, units have advanced 50 km into Russian-held territory, taking 20 settlements, according to Oleksiy Hromov, a spokesman for the Ukrainian armed forces.

"The enemy is partially demoralized but continues to put up resistance," Hromov said in a briefing on Thursday.

In his Thursday evening video address, Ukrainian President Volodymyr Zelensky said soldiers had liberated a total of 1000 km2 (386 square miles) of occupied territory since the beginning of September. Some Ukrainian units have moved so fast they're beyond the range of artillery support, according to pro-Kremlin Russian military blogger Alexander Kots.

By Friday, Kots was worried that Ukrainian forces already had cut ties with Kupyansk, a key logistics hub for Russian troops fighting in the eastern Donbas region. He said Ukrainian soldiers appeared to have veered north of the town to sever the road to the Russian border. "The situation is difficult," Kots wrote on his Telegram channel, which has more than half a million subscribers.

Further south in Kherson, however, some Russian bloggers portrayed a much more difficult scenario for their Ukrainian foes, claiming heavy casualties and a stuttering advance -- accounts supported by wounded Ukrainian soldiers interviewed by the Washington Post.

It wasn't possible to independently verify the claims by either Ukraine or the Russian bloggers, but they were unusually aligned.

A Ukrainian force spearheaded by 15 tanks moved on Balakliya on Tuesday, overwhelming eight nearby villages in less than a day and adding another the following day, Romanov Light, a Telegram blogger with over 56,000 followers, wrote on his channel.

"An advance group of special forces flies in an armored column at speed into the center of a settlement, dismounts, suppresses everything around and then holds the settlement," Romanov Light wrote, referring to armored personnel carriers.

In a post late Wednesday, he added the Russian air force had finally engaged, risking anti-aircraft fire to bomb Ukrainian units on the ground. By Thursday, however, the Ukrainian attack had claimed Shevchenkovo, the largest remaining town on the road east to Kupyansk.

While in some cases even the identities of Russian bloggers can't be verified, those cited are closely watched by Western and independent Russian military analysts for their willingness to depart from the Kremlin script and their record in chronicling the war.

The latest daily report from the Institute for the Study of War described the gulf between the Russian Defense Ministry's silence on Ukrainian gains and criticism from military bloggers as the most severe since a disastrous attempted river crossing by Moscow's forces in May. It also said Ukrainian troops would likely take Kupyansk within days.

Russia's defense ministry didn't comment on the fighting Friday, but it did release what it said was a video of tanks and other military vehicles redeploying toward Kharkiv.

How events develop further around Balakliya and Kupyansk is unclear, not least because Ukraine likely lacks the deep reserves needed to exploit any breakthrough to take and hold territory on a larger scale.

US Defense Secretary Lloyd Austin said Ukraine has been using its military capabilities, including HARM missiles, well in its current operations. "They are changing the dynamics on the battlefield," he told reporters in Prague. "We see success in Kherson, we see success in Kharkiv."

In an article on Wednesday, Ukraine's top commander Valery Zaluzhnyi cited bigger reserves of personnel and weapons as prerequisites for any counteroffensive capable of changing the course of war, projecting that this would happen in 2023.

Zaluzhnyi also singled out the Ukrainian position on the Izyum front in Kharkiv as particularly difficult for its forces to hold. Kupyansk is the logistics and transit hub for the Izyum front, about 75 km south.

Disrupting the flow of troops and supplies toward Izyum could in turn reduce the threat to Slovyansk, a key town for Russian forces to seize if they are to meet Putin's stated goal of taking all of the Donbas. "We urgently need reserves in Izyum. The forces available in the city are not enough for the assigned tasks," another Russian blogger, Zakhar Prilepin wrote on Friday.

Already on Thursday, Kupyansk was under continual artillery fire and Kremlin forces had imposed a lock down for fear of Ukrainian saboteurs, according to Wargonzo, a much-cited and fiercely partisan Russian Telegram blog that has more than 1 million subscribers.

The Kharkiv offensive has fed a more generalized gloom among many Russian commentators willing to depart from the Kremlin's relentlessly optimistic script, disappointed by what they see as the poor performance and leadership of the Russian military.

Failing a declaration of martial law and full military and economic mobilization, "I do not expect any more major successes of the (Russian) armed forces over the next 2-3 months," Igor Girkin, a Russian blogger and reputed intelligence officer who was the first commander of pro-Russia forces in Donbas in 2014, wrote on his Telegram channel this week.

Girkin, who uses the pseudonym Strelkov, is being tried in absentia for his alleged role in the July 2014 shooting down of Malaysian Airlines Flight 17, with a ruling expected in November. He has denied the accusation. His Telegram channel has 469,000 subscribers and is frequently cited by Western military analysts.

"South of Kharkov -- so far a complete 'alles Kaput' of organized defense. Balakleya abandoned by our troops. Fights are going on near approaches to Kupyansk," Girkin wrote on Friday. Previously, he described the Ukrainian offensive further south in Kherson as dangerous for Russian forces that could find themselves trapped on the West bank of the Dnipro River, but far less successful for Ukraine.

"The large losses of the advancing in people and equipment are not justified by territorial successes, not a single Russian grouping has been defeated," Girkin wrote.

The tide could also turn in the north. While the Ukrainian advances toward Kupyansk look to be a "major breakthrough," the Conflict Intelligence Team, a Russian research group that tracks the war, said in its daily bulletin on Thursday, "there are Russian reinforcements that have yet to be deployed."

Bloomberg's Aliaksandr Kudrytski and Daryna Krasnolutska contributed to this report.