Fears of a 'catastrophic' nuclear disaster have been heightened after Russian forces were accused of firing rockets at a facility with a nuclear reactor in Ukraine.
There have been reports that the Russian military has fired missiles at the Kharkiv Institute of Physics and Technology, where a nuclear reactor is held for research purposes.
Ukraine's national security service has warned that damage caused by the attack could lead to a "large scale ecological disaster".
The latest attack comes just days after Putin's forces shelled Europe's largest nuclear power plant.
Speaking about the impacts further attacks on the Institute could have on the planet Emine Dzheppar, deputy minister for foreign affairs, said the destruction of the facility would lead to an "environmental catastrophe".
He said: "The Russian aggressor fired hail at the Institute's territory, where the Neutron Source nuclear facility is located, with 37 nuclear fuel cells loaded into its core.
"Destruction of a nuclear installation and storage facilities for nuclear materials can lead to a large-scale environmental catastrophe."
The US funded the facility for research uses for medicines, industry and physics, with $70 million.
The reactors contained in the Institute are not as big as those used in nuclear power plants. However, if damaged, the facility still poses a significant risk.
Nuclear disaster is no stranger to Ukraine after the country experienced devastation following the disaster of Chernobyl in 1986.
The poorly managed Soviet Union-run facility triggered the world's worst nuclear plant catastrophe.
The disaster meant the area surrounding the plant became uninhabitable and remains radioactive to this day.
It is now feared the recklessness of Russian troops could trigger a new catastrophe as places such as the Kharkiv Institute of Physics and Technology are targeted.
Linda Thomas-Greenfield said on Friday: "Russian forces are now 20 miles, and closing, from Ukraine's second-largest nuclear facility.
"This imminent danger continues."
She asked that Moscow stop any further use of force that puts at risk all 15 reactors across Ukraine.
She said: "Nuclear facilities cannot become part of this conflict.
"Mr Putin must stop this madness, and he must stop it now."
Despite Russian troops bombing a nuclear plant on Friday, Ukraine's State Nuclear Regulatory Inspectorate said no changes in radiation levels were recorded.
However, risks remain around the damage of cooling facilities and spent fuel storage containers at the site.
