The head of the UN nuclear watchdog says a neutron generator at a physics institute in the Ukrainian city of Kharkiv has apparently been destroyed.

The head of the International Atomic Energy Agency, Rafael Mariano Grossi, said on Monday that the relatively new facility was considered “subcritical” and had “a very small inventory of material”.

There has been no release of radiation.

Mr Grossi said that the site was part of a co-operation between the US and Ukraine and produced neutrons for scientific experiments.

He added: “It’s a scientific institution, so it’s really very regrettable what happened.”

Kharkiv has been under sustained attack by Russian forces in recent days.

The International Atomic Energy Agency is also pressing forward with efforts to secure an agreement with Ukraine and Russia on the safety of Ukraine’s nuclear power stations, amid deepening concerns about the situation.

On Friday, Russian forces took control of the Zaporizhzhia station, Ukraine and Europe’s biggest, following an attack that set off a fire at a building on the site.

The International Atomic Energy Agency says Ukraine has since informed it they tightened their control, with Ukrainian staff required to seek their approval for any operation and normal communications impeded.

Mr Grossi, said on Monday the conditions are “absolutely extraordinary”, adding “there is safe operation, but there are many, many questions on the ability to sustain this for much longer if we don’t support this in some way”.

He called for commitments “not to go anywhere near a nuclear facility when it comes to military operations”.

The director-general initially proposed talks at the decommissioned Chernobyl plant, the site of the 1986 disaster, which is also controlled by Russian forces.

The Kremlin said on Sunday that Russian President Vladimir Putin believes talks could be useful in principle but suggested they could be held by video call or in a third country.