Vladimir Putin would need more than four years and lose almost two million soldiers if he wanted to capture the territory he has already declared part of Russia, according to British defence officials.
The claim comes as US President Donald Trump pushes Ukraine to accept a peace deal on Moscow’s terms, warning that Kyiv risks losing the war.
The Kremlin’s demands include full control of the Donbas region, which covers Donetsk and Luhansk, as well as parts of Zaporizhzhia and Kherson, four regions tyrannical Putin annexed illegally in 2022.
But more than two years after claiming them, Russia does not fully control any of these areas.
And new analysis from the UK’s Ministry of Defence shows Moscow is far from being able to take them by force.
The British assessment, based on current rates of advance and Ukrainian casualty estimates, says Russia would need 4.4 years and would suffer an extra 1.93 million casualties to seize control of the territories it claims to have annexed.
That would be on top of the one million troops already dead or wounded since the full-scale invasion began in February 2022.
Zelensky is adamant that Russia has come nowhere close to the goals it hoped to achieve at the start of the war and has insisted that he will not agree to a deal where Ukraine would give up land.
After the summit with Trump, an optimistic Zelensky declared: ‘The stories about them capturing our Donbas by the end of the year – that’s idle talk. To occupy our Donbas, they would need another four years.’
Ukraine’s confidence in these figures partly stems from a vast defensive system it calls the ‘fortress belt’.
It extends around 30 miles across Donetsk, from Slovyansk to Kostyantynivka and is protected by dragon’s teeth tank traps, trenches, minefields and bunkers.
The dragon’s teeth are pyramid-shaped concrete blocks designed to stop or slow down tanks and armoured vehicles.
They work by damaging tracks, immobilising vehicles, or forcing them into choke points where they become easy targets.
These defences are often combined with trenches and minefields for maximum effect.
Ukrainian forces have reinforced it since 2014, when Russia first invaded and seized Crimea. It is now considered one of the most heavily fortified zones in Europe since the Second World War.
Analysts say giving up the belt would be catastrophic for Ukraine, as it would give Russia the go-ahead for further attacks.
Matthew Savill, of the London-based think tank RUSI, has cautioned: ‘It would mean the loss of their most extensively fortified and resourced defences in the east, opening up Kharkiv and Dnipropetrovsk to future attacks.’
The Institute for the Study of War has also warned that giving up the belt would mean Ukraine would have the short end of the stick and would have no assurance that fighting would cease.
In the past 11 years, Ukraine has spent vast resources on building defences around some of the most prominent cities in the region.
Putin would be able to launch new offensives deeper into Ukraine if he were to get control, analysts believe.
The strength of the defence has not stopped Moscow from launching costly assaults.
One recent attack near Dobropillia saw Putin’s army advance more than six miles, one of their deepest pushes in months, before being surrounded by Ukraine’s elite Azov Corps.
The Azov Corps, formerly known as the 12th Special Purpose Brigade Azov, is a distinguished unit within Ukraine’s National Guard.
Established in 2014, it has evolved from a volunteer militia into an elite force recognised for its rigorous training and combat proficiency.
Azov was pivotal in defending Mariupol and is now central to Ukraine’s defensive strategy.
The unit has integrated NATO-standard tactics and training, focusing on modern warfare, including drone operations and tactical medicine.
According to Azov, 385 Russian soldiers were killed and 37 vehicles, an armoured fighting vehicle and a tank were captured in its latest show of dominance.
Although the push did not end well for the Kremlin, it demonstrated the brutal tactics Russia is using.
Shaun Pinner, the former British Marine who fought alongside Azov, says Russian soldiers are sent on what he calls ‘suicide missions’.
He said: ‘There isn’t one area of the front line that isn’t on a TV screen. It’s almost an impenetrable “iron curtain” of drones.’
He explained how small groups of soldiers move on motorbikes and electric scooters without support, trying to slip through Ukrainian lines.
The failed attack near Dobropillia was not an isolated case – Moscow has been trying for months to make meaningful gains in Donetsk but has advanced only by inches.
According to the Institute for the Study of War, Russian forces have spent nearly two years trying to capture Kupyansk and still have not completed an encirclement.
In 14 months, they were only able to advance just 6.4 miles from the eastern to western edges of Toretsk and more than two years to move 6.8 miles from western Bakhmut to the outskirts of Chasiv Yar.
Even Putin’s summer offensive, launched with fanfare, has resulted in only marginal progress despite thousands of losses.
These slow gains have sparked debate about whether Russia, not Ukraine, is closer to a breaking point.
British and US analysts believe the Kremlin faces two major vulnerabilities – its military and its economy.
Russia’s economy has already been hit by sanctions, inflation and a growing labour shortage as hundreds of thousands of young men are killed, wounded or flee conscription.
Moscow is also struggling to produce enough weapons and ammunition despite ramping up arms production and buying supplies from Iran and North Korea.
It has also been relying on North Korean leader Kim Jong Un to send in additional troops to fight in the war.
Meanwhile, Trump’s approach to negotiations has shifted the political pressure onto Kyiv rather than Moscow, analysts say.
By calling for land-for-peace deals and reducing US military aid, he has strengthened Putin’s position, even as Russian forces bleed men and equipment.
Last week, Russian soldiers trolled Ukraine by waving the US and Russian flags side by side, with the belief that the US leader is on Russia’s side.
It came after Donald Trump and Putin’s meeting, which many experts say worked in the former’s favour and was a tool to launch him back onto the world stage.
In the meantime, the British Defence Intelligence estimate of 4.4 years is not a guarantee of how the war will unfold.
For now, Ukraine’s fortress belt holds firm. Behind the dragon’s teeth and trenches, its soldiers prepare for more attacks.
Yet experts believe that every mile Russia tries to take will cost it more lives, more money and more time than the Kremlin can afford.
Analysts warn that every failed assault weakens Moscow further, straining both its military and economy.
The fortress belt continues to serve as a crucial barrier, buying Ukraine time and exacting a heavy toll on Russian forces.