US Secretary of State Antony Blinken speaks during a press conference. File photo

Secretary of State Antony Blinken said the United States was "deeply concerned" that the Zaporizhzhia plant, which Russia was accused of firing shells dangerously close to in March, was now a Russian military base used to fire on nearby Ukrainian forces.

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"Of course the Ukrainians cannot fire back lest there be a terrible accident involving the nuclear plant," Blinken told reporters after nuclear nonproliferation talks at the United Nations in New York on Monday.

Picture used for illustrative purposes only.

Russia's actions went beyond using a "human shield" Blinken said, calling it a "nuclear shield."

At the New York talks, Ukraine's Deputy Foreign Affairs Minister Mykola Tochytskyi said "robust joint actions are needed to prevent nuclear disaster" and called for the international community to "close the sky" over Ukraine's nuclear power plants with air defence systems.

Russian President Vladimir Putin's Feb. 24 invasion of Ukraine has sparked the biggest conflict in Europe since World War Two, killing thousands, displacing millions and leaving large parts of Ukraine in rubble.

The war has also caused a global food crisis, with Russia and Ukraine producing about a third of the world's wheat, while Western sanctions on Russia, a major energy provider to Europe, have caused a global energy crisis.

Reuters