Russia has recaptured half of the territory it lost to Ukraine in Kursk, a region central to Volodymyr Zelensky’s plan to defeat Vladimir Putin.

A senior Russian commander from Chechnya said that an estimated 50,000 troops were pushing back Ukrainian forces, who either had to flee or “end up in the cauldron”.

“Approximately half of the territory that was occupied by the enemy has already been liberated,” said Major General Apty Alaudinov.

Well-connected Russian and Ukrainian military bloggers have been reporting since Saturday that Moscow’s troops have punched through sectors of Ukraine’s front lines in Kursk.

Mr Zelensky has insisted that the situation has stabilised but the US-based Institute for the Study of War, which holds staunchly pro-Ukraine views, said that it has seen “visual evidence” that Russia has recaptured 46 per cent of its territory in Kursk.

According to some commentators, seasonal rain has turned the ground to mud in the Kursk region, handing Russia an advantage because its forces use more tracked vehicles than Ukrainian troops do.

Boris Rozhin, a pro-Kremlin blogger, posted a video of Ukrainian soldiers pulling an armoured car out of a rain-soaked patch of forest next to a water-logged, mud-coated track.

“Ukrainian forces are doing a lot of whining about how they have a lot of wheeled vehicles, while Russian forces are betting on tracked vehicles,” he said.

The muddy season in Russia and Ukraine is called “rasputitsa” and is renowned for bogging down vehicles on tracks and fields, making travel slow-going.

Emil Kastehelmi, an open-source research analyst at the Finland-based Black Bird Group, also said that the terrain that Ukrainian forces were trying to defend in Kursk favoured the attacker.

“The area is mostly dominated by large open fields with a limited natural cover,” he said, describing Ukraine’s western flank. “Especially without proper fortifications, defending it can be difficult.”

By Mr Kastehelmi’s reckoning, Ukraine has lost at least a third of the territory that it had once held in the Kursk region.

Ukraine launched its daring incursion into Russia in August. Catching Russian soldiers by surprise, Ukrainian forces quickly captured a region around the town of Sudzha measuring roughly 450sq miles, half the size of Dorset.

The invasion boosted morale among Ukrainian civilians but some analysts warned that instead of drawing Russian forces away from the front line, it had weakened Ukraine’s defences.

Last month, George Beebe, the director of grand strategy at the US-based Quincy Institute, said the Kursk operation was already looking like a “blunder”.

He said: “There seems to be a great deal of scepticism about what this incursion is going to accomplish.”

Regardless, Mr Zelensky has made holding on to Ukraine’s Kursk salient central to his ‘Victory Plan’, which he presented to Sir Keir Starmer last week.

But Russian forces have accelerated their attacks along the front line in Donbas since Ukraine invaded Kursk, and on Tuesday pro-Russia officials in occupied Donetsk said that they had now captured two-thirds of Toretsk, a key front-line town with a pre-war population of 34,000 people.

In the northern section of the front line in east Ukraine, Ukrainian officials have also ordered the evacuation of civilians from the city of Kupyansk on the banks of the Oskil river because of Russian advances.

Oleg Sinegubov, the head of the Kharkiv region , said: “The military situation is deteriorating and we cannot ensure the heating season, the provision of electricity, and humanitarian assistance. The enemy is shelling critical infrastructure.”