In the annals of Soviet military history, Russia's 4th Guards tank division is legendary, its reputation forged at Stalingrad and in the liberation of Poland from the Nazis.
On Saturday, it was rooted in Trostyanets, a town 350 kilometres east of Kyiv. If evidence was needed that Vladimir Putin's invasion was faltering, the images emerging from Trostyanets of burnt-out howitzers and tanks belonging to the elite division will surely shake the resolve of even the Kremlin's most loyal supporters.
Just 24 kilometres from the Russian border, Trostyanets was attacked at the start of the invasion and seized by Russian troops after a week-long battle on March 1. When the armoured vehicles rolled into Trostyanets' main square at the start of the month, their movements were caught on mobile phone footage by local residents and posted on social media.
Almost four weeks later, the same tanks and artillery units from the 4th tank division that were filmed manoeuvring into position in the town square are now burnt out, with Russian forces either captured or killed by Ukrainian troops and local guerilla forces.
After 25 days under Kremlin control, Trostyanets was once again flying the Ukrainian flag on Sunday. The significance of the victory should not be underestimated.
Trostyanets is on a main road just 50km south of Sumy, a city that has been under siege for almost a month. The counter-offensive to take it back offers hope of opening up a supply route to Sumy, which has a population of about 250,000, for military reinforcements, as well as food and medicines.
To the south of Trostyanets is Okhtyrka, a large town that has been carpet-bombed by Russia but has refused to surrender. Doing so has helped to keep open a direct route between Kyiv and Ukraine's second-largest city, Kharkiv.
Recapturing Trostyanets removes a Russian springboard for further assaults and raises serious questions about the Kremlin's ability to keep territory it has conquered.
Footage posted online on Sunday showed Ukraine troops advancing in the Sumy region, with soldiers marching on foot in battle fatigues behind the cover of an armoured vehicle firing at Russian positions.
The firefight ended with a huge explosion after a Ukrainian tank fired at the enemy. In the next scene, about 10 Russian troops, each wearing red armbands, are filmed lying face down in a field or yard with burning homes in the background. The soldiers' arms are outstretched, as each is searched by their Ukrainian captors.
"Trostyanets is free from Russian occupation," proclaimed the Facebook page of Ukraine's 93rd Mechanised Brigade, named Kholodhny Yar after the last piece of Ukrainian territory to be incorporated into the Soviet Union - four years after the Russian revolution.
Photographs posted on the page showed Ukrainian military leaders shaking hands with liberated townsfolk or posing in front of a burnt-out 2S19 Msta self-propelled howitzer - a huge gun based on a tank hull that is capable of firing 152.4mm calibre shells 24km. The howitzers had been deployed by Putin in the second Chechen war and in his invasion of eastern Ukraine in 2014.
In another photograph, four soldiers in battle fatigues posed in front of boxes of Russian ammunition piled high. Other images showed the devastation and destruction after a month's fighting.
The Facebook page went on: "Today, the 93rd Mechanised Brigade Kholodnyi Yar, with the help of territorial defence forces and local partisans, has liberated the city of Trostyanets in the Sumy region from the Russian occupation forces.
"Kholodnyi Yar fighters have managed to expel the 'elite' Russian ground force troops, the Kantemyr tank division [4th Guards]
"This was preceded by the defeat of the command post and the leadership of the 96th Separate Reconnaissance Brigade in the first days of the defence of Okhtyrka and the battles for Trostyanets.
"After a series of setbacks, the Russian army has fled Trostyanets, leaving behind weapons, equipment and ammunition that the 93rd Brigade will use to liberate other Ukrainian cities from occupation."
The Russian occupation of the town will now be subject to war crime investigations. The regional prosecutor's office in Sumy opened a file after it was claimed that Russian troops had thrown hand grenades at civilians protesting against the Kremlin takeover of the town on March 18. The blast killed two men.
Philip Ingram, a former colonel in British military intelligence, said: "Trostyanets is a town on a significant north-south route between Sumy and Okhtyrka. If Ukraine has control of that road, then you are seriously restricting Russia's ability to manoeuvre.
"Any roads Ukraine takes back impacts Russia's ability to move around. The Russians are constrained to the roads and control of the junctions gives you firing positions straight down them."
It remains unclear where the Ukrainian defensive positions are in the region. However, their ability to mount counter-attacks a month after the invasion suggests Russia has failed to land knockout blows - even in areas close to its border, where supply lines are shorter and logistics are in theory less problematic.
Mr Ingram said that a combination of hand-held anti-tank weaponry supplied by the West, mainly Javelins and N-Laws, were damaging the Russian forces, along with drone strikes. Ukrainian armoured infantry still appears to be able to manoeuvre along battle lines, with the Kremlin having failed to gain air superiority to knock out Ukrainian tanks.
Jack Watling, an expert on land warfare at the Royal United Services Institute, the London-based think-tank, said the recapture of Trostyanets "demonstrates that the Ukrainians are able to counter-attack", meaning "Russia can't assume that once they hold ground they have secured it. That limits the amount of resources they can apply to the place they are trying to take at any one time."
Yaroslav Trofimov, from The Wall Street Journal, who was born in Ukraine, described the recapturing of Trostyanets as probably the "most significant counter-offensive success so far". Only one regional capital, Chernihiv, remained encircled, he said.
Dmytro Zhyvytskyi, head of the Sumy regional administration, said basic facilities in Trostyanets - including the local hospital - had been mined by the Russians. Medical aid, as well as food and other supplies, are being organised.
With communications in and out of the town destroyed, emergency workers are being deployed to drive around the town with loudspeakers telling residents that they are no longer under Russian control and that aid will be distributed.
The full extent of the damage will only become clear in the coming days. The United Nations said on Sunday that the official civilian death toll was 1,119 fatalities, with a further 1,790 wounded since the invasion. But it said the true casualty figures would be far higher, because of the problems in corroborating figures in places such as Trostyanets, as well as the besieged port of Mariupol in the south.
Russia has lost at least 10,000 troops, with a further 30,000 to 40,000 wounded, according to Western officials - a quarter of its fighting force. The 4th Guards tank division - also known as the Kantemirovskaya Tank Division, after a village it liberated from the Germans in its "baptism of fire" in 1943 - has suffered "significant" losses, according to various reports.
Photographs posted on social media of burnt-out or abandoned vehicles involved in fighting on the road to Sumy backed up the claims. In one video, a Russian mobile kitchen truck, containing mainly potatoes and onions and even a drawer filled with jars of pickles, was left abandoned. The Russian army appears in places to simply be fleeing the battlefield.
Sofrep, a military website based in the US, describes the 4th Guards tank division as "one of the more elite armoured divisions of the Russian Ground Forces", comprising two tank regiments, a motor rifle regiment and its own air defence regiment. The division is revered in Russia to such an extent that a Moscow metro station is named Kantemirovskaya in its honour. The unit participated in the Battle of Kursk and the capture of Berlin in the Second World War.
In Kharkiv, Ukraine's second-largest city, it remains unclear if Russia has yet succeeded in cutting off supply lines. Videos posted online showed a large group of Russian troops taken prisoner of war near the city. In unverified footage from Kharkiv, circulated by pro-Kremlin supporters, it was claimed that Russian prisoners of war were being shot in the leg by Ukrainian troops after they had been captured.
South-east of Kharkiv, it was claimed a Ukrainian counter-attack captured a reloading vehicle for a thermobaric missile launcher, one of the most devastating bombs deployed by the Russian forces.
Russia continued to pound Chernihiv, the regional capital 160km north of Kyiv that has been encircled since March 10. Vladyslav Atroshenko, the mayor of the besieged city, told The Telegraph that he is now hoping for the nearby river Desna to thaw so that small boats can bring in supplies.
The ancient city of nearly 300,000 people has been almost entirely surrounded and is facing constant Russian bombardment. Up to 50 wounded civilians have been unable to evacuate to receive medical aid. Power, water and gas have largely been cut off. Supplies of food are also running low.
"We think the ice on the river will melt in a few days' time, so we will be able to use small boats to bring supplies in," Mr Atroshenko said in an interview over Zoom. "The river runs through areas that are sheltered from the Russians' view, so it is hard for them to target."
About 100,000 people are still in Chernihiv, the mayor said, with most having made a "conscious" decision to remain and defend it. The city dates back to the 9th century and has suffered extensive damage to its historic downtown market area.
"We will never surrender because we are a city with a 1,300-year history, and we have not been beaten or captured by invaders yet," added Mr Atroshenko.
With Russia bogged down and in places on the retreat, there are fears of what its president - whose decision to invade appears increasingly deranged - will do to extricate Moscow from the mess.
"Russia is in real trouble here," said Mr Ingram. "That presents a two-fold problem. They can hunker down in defence and hammer Ukraine with artillery and that could cause a lot more damage or, if they are pushed back further then Putin, with nothing to lose, could do something very nasty."