Russian forces in southern Ukraine were on the brink of collapse on Tuesday night after they retreated in the face of one of the fastest Ukrainian advances of the war so far. 

Ukrainian troops who initially broke through Russian lines on the western bank of the Dnieper river on Monday rolled into several more strategic villages. 

Prominent Russian military bloggers said a “regrouping” order had been given to avoid encirclement in the northern part of the Kherson region.

The significant territorial losses suffered by Russian forces appeared to be confirmed in maps used in the background of Moscow’s ministry of defence in its daily briefing, although it did not directly address the changes to the frontline.

It comes after weeks of Ukraine seeking to degrade Russia’s forces in the Kherson bridgehead by attacking the two bridges supplying them with US-provided Himars rocket systems, part of a long-awaited counter-offensive to retake the vital southern city.

Although the attacks initially made slow progress, early gains were reported this week along the bank of the Dnipro, with Ukrainian forces on Monday pressing south in the direction of the riverside town of Dudchany. 

Advances accelerated throughout Tuesday after the Russians apparently decided not to fight.

“Due to the breakthrough of the armed forces of Ukraine in the Berislav sector and the threat of physical encirclement a decision was made to withdraw the Russian group of forces from Dudchany and Davydov Brod,” Rybar, a widely read but unofficial Russian propaganda account, reported.

Like clockwork, Russia’s defence ministry pulls its old trick of confirming major losses since yesterday in Kherson & the east by showing them, otherwise totally unacknowledged, on the maps on the background of its daily video briefing

— Felix Light (@felix_light) October 4, 2022

Ukraine covered as much as 15 miles in the space of two days and said more than 50 settlements and approximately 3,500 citizens had been freed from Russian occupation.

Western officials attributed much of Kyiv’s sudden success to its forces’ ability to penetrate Russia's so-called “OODA Loop”.

The well-known military technique, developed by American military strategist John Boyd, stands for observe, orientate, decide and act.

“The Ukrainian armed forces commanders in the south and east are throwing problems at the Russian chain of command faster than the Russians can effectively respond," an official said on Tuesday as the southern offensive appeared to make gains.

“And this is compounding the existing dysfunction within the Russian invasion force."

On the northwestern side of the salient Ukrainian forces crossed the Inhulets river to seize the towns of Davydov Brod, Novo Olenivka, and Staroselye. 

Ukrainian soldiers were photographed in each of those villages hours after local residents posted pictures of themselves raising the Ukrainian flag, indicating the Russians had left. 

The Inhulets have been the scene of heavy fighting since August, with the Russians trying to maintain it as a natural line of defence against the Ukrainian offensive.

Kirill Stremousov, the Moscow-appointed deputy head of the Kherson region, told residents there was “no reason to panic”.

“Our artillery and fighter jets are hitting enemy forces that enter the sovereign territory of Russia,” he said. “Yes, you can hear explosions at a distance, but they’re infrequent.”

The Russian ministry of defence claimed in an afternoon briefing that it had destroyed “nine tanks, 12 infantry fighting vehicles, 20 vehicles and 250 personnel” in the area of the fighting but made no mention of a retreat. 

Russian commanders are expected to try to stabilise the line before the Ukrainians reach Nova Khakova, the site of a hydroelectric dam that also serves as a road bridge across the Dnieper river.

Failure to do so could lead to a general collapse of the Russian army group west of the Dnieper. 

Novakhakova is one of only two bridges the Russians are able to use to supply the troops on the western bank of the river. 

The other, the Anontonsky bridge in Kherson city, has been rendered all but unusable by Ukrainian Himars strikes. 

The Novokhakova dam lies about 33 miles southwest of Dudchany and is deemed a key target for Ukraine's forces.

The apparent retreat came as Russia’s Federation Council on Tuesday ratified the formal annexation of four occupied territories in Ukraine, including the southern Kherson region.

In response, Volodymyr Zelensky, the Ukrainian president, signed a decree formally ruling out peace talks with Russia.