Footage circulated on social media appeared to show a blaze at the Kharkiv Institute of Physics and Technology.

There are unconfirmed reports the facility was hit by a Russian air strike.

Russia has previously been accused of firing rockets at the site, which is home to the Neutron Source research facility, a facility said to have 37 nuclear fuel cells.

‘The building contains equipment which, if damaged, can lead to radioactive pollution of the environment.’

According to Ukrainian media, the fire began after air raid sirens sounded in the city at about 8.20pm.

Pravda.com.ua reported ‘citizens reported the sounds of explosions and volleys of artillery from the Russian occupiers’.

Russia has drawn international condemnation for risking environmental disaster by carrying out military operations in the vicinity of dangerous materials throughout the conflict.

Kremlin-linked media has also pushed fabricated claims Ukraine could stage a nuclear incident in Kharkiv to create a pretext for Western intervention.

The worry development comes after Boris Johnson joined a chorus of Western leaders voicing concern Russia could be planning a chemical attack.

Moscow has pushed unfounded claims Kyiv is illicitly developing weapons of mass destruction.

Western allies fear the narrative is being constructed as a pretext for an attack launched by Russia.

Addressing the reports, Mr Johnson told Sky: ‘The stuff that you’re hearing about chemical weapons is straight out of their playbook.

‘They start saying that there are chemical weapons that have been stored by their opponents or by the Americans.

‘And so when they themselves deploy chemical weapons, as I fear they may, they have a sort of maskirovka – a fake story – ready to go.

‘You’ve seen it in Syria. You saw it even in the UK. That’s what they’re already doing. It is a cynical, barbaric government.’