The Deputy Prime Minister of Ukraine, Iryna Vereschuk, has told the ABC's Four Corners that the world faces a potential nuclear catastrophe at the Chernobyl nuclear power station after shelling cut power to the Ukrainian plant.
"Last time it was one reactor, now it’s four and none of them have power," Ms Vereschuk, said, adding that Russian military action had blocked access to the site.
Ukraine's Foreign Minister Dmytro Kuleba called for a ceasefire to fix power issues and said reserve diesel generators could power the plant for 48 hours but after that he would be concerned about radiation leaks.
However the United Nations’ International Atomic Energy Agency (IAEA) said it was informed of the loss of power at the nuclear plant but that it presented no "critical impact on safety".
However the agency said the development at the plant violated a "key safety pillar on insuring uninterrupted power supply".
The agency had earlier reported it had lost communication with sensors at the plant.
The Ukrainian National Power Company, UKRENERGO, issued a statement saying because of "Russian Occupiers" the Chernobyl power plant was fully disconnected from the power grid and the plant has no power supply.
One key issue is the 20,000 used fuel rods kept at the site.
The Ukrainian energy regulator, Energoatom, had a grimmer assessment than IAEA, saying the 20,000 spent fuel rods at the facility needed constant cooling, using electricity.
The IAEA said the heat load of spent fuel and the volume of cooling water at the site meant cooling could occur without electricity supply.
Speaking to the ABC from the heavily fortified presidential headquarters in central Kyiv, Ms Vereschuk said her Russian counterparts had not responded to urgent messages requesting access to the Chernobyl site.
"This is a threat not only to Ukraine but to Russia and the whole world," she said.
When asked what her government's next move would be, Ms Vereschuk said: "We're going to call an emergency session of the UN.
"We're going to address world leaders and international organisations. And that is being done as we speak."
