Fears have grown over Russia's use of thermobaric weapons after Ukraine's ambassador to the US said a "vacuum bomb" - another term for the weapon - was used during the invasion.
The use of such weapons, which absorb oxygen from the surrounding air to generate a high-temperature explosion, has yet to be independently confirmed, although footage from Ukraine has shown thermobaric rocket launchers on Russian TOS-1 vehicles.
Marcus Hellyer, senior analyst at the Australian Strategic Policy Institute, said that while it was not clear whether they had been used by Russia in Ukraine, it was only a "matter of time" before their use began.
How do they work?
The thermobaric gun, also known as an aerosol bomb, is a two-stage munition.
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The first stage charge delivers an aerosol composed of a very fine material. The second charge ignites it, creating a fireball, huge shockwave and vacuum as it absorbs all the surrounding oxygen.
The blast wave can last much longer than a conventional explosive and is capable of vaporizing human bodies.
Such guns are used for various purposes and come in a variety of sizes. Hellyer says what we may see in Ukraine is Russia using them in a "bunker-buster" role to destroy defensive positions. Extremely large, air-launched versions are designed to destroy caves and tunnels.
Where are they used?
The bombs have been used by Russian and Western forces since the 1960s. The US relied on them in its efforts to eliminate al-Qaeda in the mountains of Afghanistan. Hellyer said Russia had a longer history with them than the West.
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"Russia has systems across the spectrum... from fairly small tactical weapons, to large, air-launched bombs. The separatists that Russia was supporting in the Donbass region, they have been using them for several years," said Hellyer.
In 2000, Human Rights Watch condemned Russia's reported use of weapons a year earlier in Chechnya as "a dangerous escalation" with "significant humanitarian implications".
How dangerous are they?
Hellyer said thermobaric weapons were effective in their "specific purpose" of "primarily destroying defensive positions." While they are not used to penetrate a tank, they could be a "very destructive weapon" against a residential building.
"They are not illegal although their effects can be quite horrific, due to that effect of creating a vacuum and sucking air out of the lungs of potential victims," he said.
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As their use is "pretty standard" in terms of Russian tactics, Hellyer said he expected to see more thermobaric warfare in Ukraine.
"One of the things we know about Russian tactics is that they are willing to destroy everything. "It's clear that the Ukrainians are hiding in bunkers in some of the cities... as this continues, the Russians will increasingly use whatever weapons they have, including thermobaric weapons in urban built-up areas," Hellyer concluded.
