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The British Ministry of Defence has said Russian officials have confirmed the use of TOS-1A weapons system, which fires thermobaric rockets.
“The Russian [Defence Ministry] has confirmed the use of the TOS-1A weapon system in Ukraine,” the British ministry said on Twitter.
“The TOS-1A uses thermobaric rockets, creating incendiary and blast effects.”
Thermobaric weapons consist of a fuel container and two explosive charges. The first detonates to disperse the fuel particles and the second ignites the fuel and oxygen in the air.
It creates a blast wave of extreme pressure and heat that creates a partial vacuum in an enclosed space.
The Russian TOS-1 Buratino multiple-launch rocket system consists of a box of rockets mounted on a tank chassis, and can rain 24 220 millimetre thermobaric rockets on enemy positions.
It is a terrifying prospect in an urban war where hundreds of civilians have already become casualties.
But the system has a relatively short range, designed to engage targets within about 6,000 metres, unlike conventional artillery that can be tens of kilometres from the front lines.
It was not immediately known where the Russian Ministry of Defence admitted to firing the weapon.
Ukrainian President Volodymyr Zelenskyy accused Russia on Wednesday of an air strike on a hospital in the southern port city of Mariupol, in which he said children were among those “under the wreckage".
Mariupol's city council said the hospital had been destroyed. It said it did not have a casualty figure but: “The destruction is colossal.”
The US government is consulting with allies on ways to boost Ukraine’s air defence as reports surface that Russia could be dropping “dumb munitions”, the Pentagon said on Wednesday.
US Secretary of State Antony Blinken said the war would become a strategic failure for Russian President Vladimir Putin.
“If his goal is to impose some kind of puppet regime by displacing the existing government and putting in place one to his liking, I think it’s pretty evident by the response of the Ukrainian people that they will never accept that,” Mr Blinken said.
The Pentagon has said that Russian mobile launchers for thermobaric weapons have been seen in Ukraine.