Ukrainian soldiers have captured a Russian rocket launcher capable of firing thermobaric weapons and used it against invading troops for the first time, according to officials.

Sergei Bratchuk, the Ukrainian spokesman for the region of Odesa, said that a TOS-1A rocket launcher — previously spotted in Russian armoured convoys during the failed assault on Kyiv — had been fired at Russian troops near Izyum, in eastern Ukraine.

The tracked vehicle fires “vacuum bombs” that suck in oxygen to create a devastating high-temperature blast that can damage internal organs.

There has been mounting evidence of Ukrainians capturing the launchers, referred to by the Russians as solntsepyok or “blazing sun”, in recent days.

Ukrainian troops posed for a photo with a captured TOS-1A unit in an image that was widely shared online this week. A Ukrainian tractor was filmed dragging another of the rocket launchers through a field. Separately, Ukrainian soldiers were seen salvaging the rotary blades from a downed KA-52 helicopter.

The TOS-1 was developed by the Soviet Union for use in Afghanistan. The updated model captured by the Ukrainian troops has 24 barrels and a range of more than six miles.

The thermobaric warheads can produce a devastating explosion with a blast radius significantly larger than conventional weaponry. They disperse an incendiary aerosol into the air which is then set alight, creating a huge fireball that sucks up oxygen from the atmosphere.

Izyum has become a crucial battlefield in the war as Russian troops attempt to encircle Donbas. The city stands between two Russian groups pushing southeast from Kharkiv and northwest from Luhansk. About 80 per cent of the city has been destroyed, according to local officials, with about 15,000 to 20,000 civilians still trapped in the town.

Ukrainian forces have so far halted the Russian advance by destroying the bridges that cross the Severniy Donets, although the invading troops are now attempting to build new crossings over the river that cuts the city in two.