Russia could use savage superweapons that vaporize bodies and crush internal organs if their assault of Ukraine becomes bogged down, Western officials warned tonight.

They fear Vladimir Putin could resort to high-power thermobaric weapons – dubbed the ‘father of all bombs’ – as brave Ukrainians resist his attempts to take control of Kyiv. There are also concerns that units that are running behind schedule as they encounter stiff opposition could resort to indiscriminate shelling as a terror weapon.

Thermobaric weapons – also known as vacuum bombs – are high-powered explosive that use the atmosphere itself as part of the explosion. They are among the most powerful non-nuclear weapons ever developed. A thermobaric bomb dropped by the US on Taliban in Afghanistan in 2017 weighed 21,600 pounds and left a crater more than 300 meters (1,000 feet) wide after it exploded six feet above the ground.

According to the Journal of Military and Veterans’ Health, Thermobaric weapons “produce more heat and overpressure than conventional explosives by exploding a vapor in the blast zone.” It adds: “Their medical effect is principally primary blast and they affect organs where there is a tissue interface of varying densities, such as the lungs, bowel, and inner ear.

“Damage manifests itself in the severity and onset of occurrence, depending on distance from the blast and orientation of the victim, and can be diagnosed by simple investigative techniques.” In 2017, a thermobaric bomb was dropped on the Taliban by US forces in Afghanistan. The bomb, which weighed nearly 10,000 kilos, left a crater of more than 300 meters.

‘My fear would be that if they don’t meet their timescale and objectives they would be indiscriminate in their use of violence,’ the official said. ‘They don’t adhere to the same principles of necessity and proportionality and rule of law that Western forces do.’

The bomb works by using oxygen from the surrounding air to generate a high-temperature explosion, making it far deadlier than a conventional weapon. While Russian special forces have reached the suburbs of Kyiv, the bulk of Russia’s heavy armor is believed to be still more than 50km away from the capital.

Western officials have suggested Russia will kill Ukrainian President Volodymyr Zelensky and his ministers if they seize Kyiv. Russia is launching a massive amphibious assault to bring thousands of navy personnel ashore in Ukraine on Friday, as Kyiv puts up a more aggressive defense than Moscow ever expected.