Ukraine's forces continued their rapid advance in the Kharkiv region on Sunday, exploiting an extraordinary collapse of Russian defenses and raising the question of how far they can go.
Unconfirmed reports overnight suggested Kyiv's troops had taken Velykyi Burluk, a town about 90 km (56 miles) east of Kharkiv and not far from the Russia-Ukraine border. The town of Chkalovske was also retaken, and all eyes are on strategically located Izyum.
Russia's Defense Ministry on Sunday published a map showing much of the country's forces out of the Kharkiv region, without commenting further.
"We are starting to advance not only to the south and to the east in the Kharkiv areas but also to the north. 50 kilometers is left until we reach the state border," Ukraine's top commander Valery Zaluzhnyi said in a Telegram post.
Zaluzhnyi said his forces had returned 3,000 sq km (1,158 square miles) of lost territory to Ukrainian control since the beginning of September. Estimates of regained ground have risen steadily in recent days.
The advance represents Ukraine's biggest victory since they pushed Russian troops away from the capitol Kyiv in March, and the past few days have been termed among the most consequential of the now 200-day invasion.
Ukraine's troops have clearly demonstrated their ability to conduct a major counteroffensive and change the course of the conflict, ahead of a difficult winter for European allies supporting Kyiv's war effort with weapons and cash.
Yet the advances also present Ukrainian commanders and leaders with some tough decisions, as they decide when to halt their advance.
"When you are pursuing an enemy that is broken, there is always significant risk that you become overstretched and expose your flanks," said Jack Watling, senior research fellow for land warfare at the Royal United Services Institute in London.
Watling described the Ukrainian commander in the Kharkiv theater as careful and unlikely to get carried away, meaning the counteroffensive will likely slow to consolidate, and leave any attempt to completely sweep Russian forces out of the region until 2023.
The speed of the rout has likely surprised the Ukrainians themselves, who had aimed to sever critical supply lines to Russian forces in Izyum, a key launching point for the Russian offensive in the eastern Donbas region. Instead, the Russian forces fled.
"Russian morale is very low and when morale is low then a shock can lead to disintegration," Watling said. "The Russians collapsed and withdrew altogether, and I am sure the Ukrainians were not expecting that."
The Institute for the Study of War, a US-based think tank, said Ukraine was likely to capture Izyum in the next day or two "if they have not already done so." Ukraine's troops have indeed taken Izyum, Mykyta Karakay, a national guard serviceman and former deputy of Izyum council, said on national television. The claim couldn't be immediately verified.
Russia's defense ministry on Saturday confirmed troop withdrawals from the region, yet cast the move as part of a plan to redeploy forces further east to to "achieve the stated goals of liberating Donbas."
On Sunday, the ministry made no mention of the retreat in a regular televised briefing, but showed a map that indicated Moscow's forces had pulled out of much of the territory they recently held in the Kharkiv region.
In Kyiv, Ukrainian President Volodymyr Zelenskiy on Saturday held the latest in a series of meetings with his top military commanders, intelligence officials, cabinet officers and advisers.
Outwardly, the Kremlin has showed no signs of panic. Russian President Vladimir Putin on Saturday kept to his announced schedule, including presiding over the opening of a new boxing gym and giant Ferris wheel at a Moscow park. Authorities in Moscow held a huge fireworks display Saturday night to mark the anniversary of the city's founding.
On Sunday, Putin spoke with French President Emmanuel Macron, who urged Russia to withdraw weaponry from around the Zaporizhzhia nuclear power plant, some 350 kilometers southwest of Kharkiv. The pair spoke after the last operating unit at the Russian-occupied facility was shut safely -- dialing back, for now, the "precarious" danger level cited on Friday by the UN's atomic agency.
"We should watch for some unexpected reaction from Putin," said Mick Ryan, a retired Australian army general who tweets about military strategy under the handle @WarintheFuture. "He (unlike some of his senior military officers) has shown no signs of believing the invasion is in trouble."
Russian military bloggers and others typically loyal to the Kremlin have started to voice criticism of how Putin's war -- designed to overrun Ukraine within days or weeks, and now at its 200th day -- has been executed.
Daniil Bezsonov, first deputy minister of information for the Moscow-backed Donetsk People's Republic in Donbas, said Saturday that the Russian military had abandoned Izyum and some other localities in Kharkiv.
"Of course, this is the result of high command mistakes," he said on his Telegram channel.
Russia's suggestion that its retreat had been planned also raised eyebrows from staunch Kremlin backers.
Chechen strongman Ramzan Kadyrov, who's sent thousands of his fighters to the front, criticized Russian authorities for failing to prepare the public for the sudden apparent reversal. "Mistakes were made," he said in a rambling late-night Telegram post on Saturday.
"If today or tomorrow changes aren't made to the strategy of the special military operation, I will be forced to contact the leadership of the Defense Ministry and the leadership of the country and explain the real situation on the ground," Kadyrov said.
Mykola Bielieskov, research fellow at the National Institute for Strategic Studies in Kyiv, said Ukraine's military will weigh the next steps carefully.
"We still need to consolidate the gains and to clear settlements, to liberate Izyum, ensure the security of the flank from the north, from the Russians in Belgorod," Bielieskov said. "So I would say it is better to be conservative and consolidate the gains, because to go further there are risks."
The Russian collapse in the north was in part because forces had been cannibalized to reinforce Russian positions against a counteroffensive in the Kherson region in the south, Bielieskov said.
"The Russians didn't have the usual defense in depth," said Bielieskov. "So as soon as the first line was broken there was a void."
Almost as important as the territory regained -- and relief for Ukrainian forces in the Donbas city of Slovyansk that had been threatened from Izyum -- is that the signal sent by the last few days of rapid reversals to Russian troops and Ukraine's backers in the US and Europe.
Faced with spiraling energy prices and likely recessions caused in part by sanctions imposed on Russia after its invasion, the proof of Ukraine's ability to recover territory could prove crucial to its continued support.
"Remember that the consensus in summer was that there would be a stalemate and the lines would fix because the Ukrainians would not be capable of a breakthrough," Bielieskov said. "Well, the strategic importance of what is happening now is that we have proved that consensus wrong."
That makes it all the more important for the last week's gains to stick, but also that Ukraine's partners draw the right lessons, according to Bielieskov.
"We still need surface to air missiles, to protect against maneuvers of attack helicopters and combat aircraft; we still need heavy artillery, because they have so much more; we still need heavy armor and mobility," he said. "We managed to do it despite a deficit, but we have a deficit.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)