Russia has confirmed it has used thermobaric weapons in Ukraine, according to the UK’s Ministry of Defence.
It said its Russian counterpart said the TOS-1A weapon system had been deployed.
The UK MoD said the system uses thermobaric rockets, creating incendiary and blast effects.
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Thermobaric weapons suck in oxygen from the surrounding air to generate a high-temperature explosion, typically producing a blast wave of a significantly longer duration than that of a conventional explosive.
They are capable of vaporising human bodies.
Last week, a Russian-language account on the Telegram messaging app identified what open-source analysts said appeared to be a Russian TOS-1A thermobaric multiple launch rocket system on a road between Kyiv and the town of Sumy.
It comes as Defence Secretary Ben Wallace has announced the UK government will send more weapons to Ukraine, including fresh supplies of anti-tank missiles.
He told MPs the UK has delivered 3,615 anti-tank (NLAW) weapons and will soon be supplying a “small consignment” of Javelin anti-tank missiles.
He said the Russians are “changing their tactics and so the Ukrainians need to too”, to help Ukraine forces tackle President Putin’s air force.
Mr Wallace also said the UK will soon be supplying a “small consignment” of Javelin anti-tank missiles and exploring the possibility of donating Starstreak anti-aircraft missiles to Ukraine.
Supplies of rations, medical equipment and other non-lethal military aid will also be increased, the defence secretary said.