Ukraine has reported the use of a thermobaric weapon by Russia during its invasion of the country.

鈥淭hey used the vacuum bomb today,鈥� Ukraine鈥檚 ambassador to the U.S. said Monday. 鈥淭he devastation that Russia is trying to inflict on Ukraine is large.鈥�

Known as vacuum bombs, aerosol bombs, or fuel-air explosives, thermobaric weapons use oxygen from the surrounding air to create massive, high-temperature explosions.

Launched as rockets or dropped as bombs, they generally work in two stages: first, a charge disperses fuel into the air to create a cloud that can flow into and around structures; then a second explosion detonates the cloud to create a powerful and extremely hot blast wave.

鈥淲hen used they utilize a huge amount of pressure to destroy buildings and fixed defensive positions,鈥� Dr. Matthew Powell told CTVNews.ca. 鈥淭he effect of these weapons is likened to that of a small-yield nuclear weapon without the residual radiation.鈥�

Powell is a historian and air power expert who teaches at the U.K.'s Royal Air Force College as part of the University of Portsmouth's military education team.

鈥淭he effect on civilian populations can be brutal,鈥� Powell explained. 鈥淭heir very nature means they are not precision weapons and do not discriminate in terms of whether combatants or non-combatants are affected by them.鈥�

Derived from the Greek words for 鈥渉eat鈥� and 鈥減ressure,鈥� thermobaric weapons are more powerful than similarly-sized conventional explosives and have been used with devastating effect as a so-called 鈥渂unker buster鈥� to destroy fortifications, tunnels and caves.

The weapons first saw widespread use in the hands of the U.S. during the Vietnam War and have since been utilized by both the U.S. and Russia in Afghanistan, and by Russia and its allies in Syria.

Human Rights Watch decried their deployment by Russia in the 1999 to 2000 war in Chechnya as 鈥渁 dangerous escalation鈥� with important humanitarian implications.鈥�

鈥淚n urban settings it is very difficult to limit the effect of this weapon to combatants, and the nature of [thermobaric weapon] explosions makes it virtually impossible for civilians to take shelter from their destructive effect,鈥� the group said in a Dec. 1999 report.

That report also cited a CIA study that described the weapons鈥� 鈥渋mmense鈥� effects on people in confined spaces.

鈥淭hose near the ignition point are obliterated,鈥� it reads. 鈥淭hose at the fringe are likely to suffer many internal, and thus invisible injuries, including burst eardrums and crushed inner ear organs, severe concussions, ruptured lungs and internal organs, and possibly blindness.鈥�

On Saturday, spotting an armoured vehicle in southern Russia that was apparently equipped with a thermobaric rocket launching system.

N.R. Jenzen-Jones is the director of , a specialist technical intelligence consultancy.

鈥淩ussia has developed a range of thermobaric munitions鈥攆rom man-portable recoilless weapons to large air-delivered bombs鈥攎any of which draw upon military lessons learned during intense urban fighting during the conflicts in Chechnya,鈥� Jenzen-Jones told CTVNews.ca. 鈥淲hen used by Western armed forces鈥� thermobaric munitions are typically either very small or use precision guidance to minimize the risk of collateral harm.鈥�

Russian attacks have killed hundreds of civilians since the Feb. 24 invasion. To Powell, the use of thermobaric weapons in population centres could warrant war crimes charges.

鈥淭heir use in towns and cities against civilian targets would breach the internationally recognized laws of armed conflict and potentially be classed as crimes against humanity due to the devastation they can cause on concentrated populations in large built-up areas,鈥� Powell said.

鈥淭he Russian resort to using thermobaric weapons may suggest that their initial estimations for operations against Ukraine have failed badly and they need to increase the level of force and violence utilized in order to achieve their military and, ultimately, political goals.鈥�

With files from Reuters