The United States said Russia was using Ukraine's biggest nuclear power plant as a "nuclear shield" by stationing troops there, preventing Ukrainian forces from returning fire and risking a terrible nuclear accident.
US Secretary of State Antony Blinken said Washington 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.
"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.
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 one third of the world's wheat, and Western sanctions on Russia, a major energy provider to Europe, have caused a global energy crisis.
FIRST GRAINS SHIPS
The first ship to carry Ukrainian grain through the Black Sea since Russia invaded Ukraine five months ago left the port of Odesa for Lebanon on Monday under a safe passage deal.
The sailing was made possible after Turkey and the United Nations brokered a grain and fertiliser export agreement between Russia and Ukraine last month - a rare diplomatic breakthrough in a conflict that has become a drawn-out war of attrition.
The Sierra Leone-flagged ship Razoni will head to the port of Tripoli, Lebanon, after transiting Turkey's Bosphorus Strait linking the Black Sea, which is dominated by Russia's navy, to the Mediterranean. It is carrying 26,527 tonnes of corn.
But there are still hurdles to overcome before millions of tonnes of Ukrainian grain depart from its Black Sea ports, including clearing sea mines and creating a framework for vessels to safely enter the conflict zone and pick up cargoes.
The United Nations has warned of the risk of multiple famines this year due to the war in Ukraine.
Known as Europe's breadbasket, Ukraine hopes to export 20 million tonnes of grain held in silos and 40 million tonnes from the harvest now under way, initially from Odesa and nearby Pivdennyi and Chornomorsk, to help clear the silos for the new crop.
Moscow called the Razoni's departure "very positive" news, but it has denied responsibility for the food crisis, saying Western sanctions have slowed its exports and accusing Ukraine of laying underwater mines at entrance of its ports.
Russia and Ukraine accuse each other of laying the mines that now float around the Black Sea, drifting far from Ukraine's shores, with Romanian, Bulgarian and Turkish military diving teams defusing those that have ended up in their waters.
Russia invaded Ukraine in what it called a "special operation" to demilitarise its neighbour. Ukraine and Western nations have dismissed this as a baseless pretext for war.
After failing to capture the capital Kyiv early in the war, Russia now aims to capture the eastern Donbas region, made up of Donetsk and Luhansk, partially occupied by Russia-backed separatists before the invasion, and capture more of the south, having already annexed Crimea from Ukraine in 2014.
Ukrainian presidential adviser Oleksiy Arestovych said in an interview posted on line about 22,000 Russian troops were preparing to advance on the cities of Kriviy Rih and Mykolaiv, where a "sufficiently large" Ukrainian force lay in wait.
In Kherson region, which is mostly under Russian control, Ukrainian troops had liberated some 50 towns, said Yuri Sobolevsky, deputy head of the ousted Kherson regional council.
"Russian troop in Kherson region are sustaining considerable losses. There are now more than 300 in a military hospital that the Russians have set up in a civil hospital in the town of Beryslav," Sobolevsky wrote on Telegram. "About 40 doctors have been brought in from Russia to staff the hospital."
Reuters was unable to verify the battlefield report.
Serhiy Gaidai, governor of Luhansk region, which is nearly all under Russian control, said foreign fighters were arriving.
"We have noticed that more and more private military companies coming into the area -- the Wagner group," Gaidai told Ukrainian TV, adding that these irregular forces were motivated by "money and looting."
Russian private military firm Wagner has likely been allocated responsibility for specific sectors of the front line in eastern Ukraine, possibly as Russia is facing a major shortage of combat infantry, Britain's Ministry of Defence said in an intelligence update on Friday.
Gaidai said partisans were destroying key infrastructure, including gas and water networks, in battered Luhansk towns to slow Russian forces.