By Vasilisa Stepanenko And Susie Blann in Kherson

KHERSON, Ukraine (AP) — A major dam in southern Ukraine collapsed Tuesday, triggering floods, endangering crops in the country’s breadbasket and threatening drinking water supplies as both sides in the war scrambled to evacuate residents and blamed each other for the destruction.

Ukraine accused Russian forces of blowing up the Kakhovka dam and hydroelectric power station on the Dnieper River in an area that Moscow has controlled for over a year, while Russian officials blamed Ukrainian bombardment in the contested area. It was not possible to verify the claims.

The environmental and social consequences quickly became clear as homes, streets and businesses flooded downstream and emergency crews began evacuations; officials monitored cooling systems at the Zaporizhzhia Nuclear Power Plant; and authorities expressed concern about supplies of drinking water to the south in Crimea, which Russia illegally annexed in 2014.

In the downstream city of Kherson, a woman who gave her name only as Tetyana waded through thigh-deep water to reach her flooded house and rescue her dogs. They were standing on any dry surface they could find but one pregnant dog was missing. “It’s a nightmare,” she kept repeating, declining to give her full name.

Both Russian and Ukrainian authorities brought in trains and buses for residents. About 22,000 people live in areas at risk of flooding in Russian-controlled areas, while 16,000 live in the most critical zone in Ukrainian-held territory, according to official tallies. Neither side reported any deaths or injuries.

A satellite photo Tuesday morning by Planet Labs PBC analyzed by The Associated Press showed a large portion of the dam’s wall, more than 600 meters (over 1,900 feet), missing.

The dam break added a stunning new dimension to Russia’s war, now in its 16th month. Ukrainian forces were widely seen to be moving forward with a long-anticipated counteroffensive in patches along more than 1,000 kilometers (621 miles) of front line in the east and south.

It was not immediately clear whether either side benefits from the dam’s collapse, since both Russian-controlled and Ukrainian-held lands are at risk. The damage could also hinder Ukraine’s counteroffensive in the south and distract its government, while Russia depends on the dam to supply water to Crimea.

Although Kyiv officials claimed Russia blew it up to hinder the counteroffensive, observers note that crossing the broad Dnieper would be extremely challenging for the Ukrainian military. Other sectors of the front line are more likely avenues of attack, analysts say.

Even so, Nigel Gould-Davies, a senior fellow for Russia and Eurasia at the International Institute for Strategic Studies, said the alleged Russian destruction of the dam “betrays a lack of confidence, a profoundly defensive measure, the lack of confidence in Russia’s longer-term prospects” in the war.

Experts have previously said the dam was in disrepair, which could also have led to the breach. David Helms, a retired American scientist who has monitored the reservoir since the war began, said in an email that it wasn’t clear if the damage was deliberate or simple neglect from Russian forces occupying the facility.

But Helms also noted a Russian history of attacking dams.

Underscoring the global repercussions, wheat prices jumped 3% after the collapse. It’s unclear whether the surge in wheat prices was due to a real threat of floodwaters destroying crops. Ukraine and Russia are key global suppliers of wheat, barley, sunflower oil and other food to Africa, the Middle East and parts of Asia.

Authorities, experts and residents have expressed concern for months about water flowing through — and over — the Kakhovka dam. After heavy rains and snow melt last month, water levels rose beyond normal, flooding nearby villages. Satellite images showed water washing over damaged sluice gates.

Amid official outrage, Ukrainian President Volodymyr Zelenskyy convened an urgent meeting of the National Security Council. He alleged Russian forces set off a blast inside the dam structure at 2:50 a.m. (2350 GMT Monday, 7:50 p.m. EDT Monday) and said about 80 settlements were in danger. Zelenskyy said in October that Russia had mined the dam and power plant.

But Kremlin spokesman Dmitry Peskov called it “a deliberate act of sabotage by the Ukrainian side … aimed at cutting water supplies to Crimea.”

White House officials were trying to assess potential impacts of the dam collapse and were looking to see what humanitarian assistance can be provided to Ukrainians who are being displaced, according to a U.S. official who spoke on condition of anonymity and was not authorized to comment publicly.

Both sides warned of a looming environmental disaster. Ukraine’s Presidential Office said some 150 metric tons of oil escaped from the dam machinery and that another 300 metric tons could still leak out.

Andriy Yermak, the head of Ukraine’s President’s Office, posted video showing the flooded streets of Russian-occupied Nova Kakhovka, a city in the Kherson region where about 45,000 people lived before the war.

Ukraine’s Interior Ministry urged residents of 10 villages on the Dnieper’s right bank and parts of the city of Kherson to gather essential documents and pets, turn off appliances, and leave, while cautioning against possible disinformation.

The Russian-installed mayor of occupied Nova Kakhovka, Vladimir Leontyev, said it was being evacuated as water poured in.

Ukraine’s nuclear operator Energoatom said via Telegram that the damage to the dam “could have negative consequences” for the Zaporizhzhia Nuclear Power Plant, which is Europe’s biggest, but wrote that for now the situation is “controllable.”

The U.N.’s International Atomic Energy Agency said there was “no immediate risk to the safety of the plant,” which has been shut down for months but still needs water for its cooling system. It said that IAEA staff on site have been told the dam level is falling by 5 centimeters (2 inches) an hour. At that rate, the supply from the reservoir should last a few days, it said.

The plant also has alternative sources of water, including a large cooling pond than can provide water “for some months,” the statement said.

Ukrainian authorities have previously warned that the dam’s failure could unleash 18 million cubic meters (4.8 billion gallons) of water and flood Kherson and dozens of other areas where thousands live.

The World Data Center for Geoinformatics and Sustainable Development, a Ukrainian nongovernmental organization, estimated that nearly 100 villages and towns would be flooded. It also reckoned that the water level would start dropping only after 5-7 days.

A total collapse in the dam would wash away much of the broad river’s left bank, according to the Ukraine War Environmental Consequences Working Group, an organization of environmental activists and experts documenting the war’s environmental effects.

Mykhailo Podolyak, a senior adviser to Zelenskyy, said that “a global ecological disaster is playing out now, online, and thousands of animals and ecosystems will be destroyed in the next few hours.”

Video posted online showed floodwaters inundating a long roadway; another showed a beaver scurrying for high ground.

The incident also drew international condemnation, including from German Chancellor Olaf Scholz and NATO Secretary-General Jens Stoltenberg, who said the “outrageous act … demonstrates once again the brutality of Russia’s war in Ukraine.”

Ukraine controls five of the six dams along the Dnieper, which runs from its northern border with Belarus down to the Black Sea and is crucial for the country’s drinking water and power supply.

Ukraine’s state hydro power generating company said the dam’s power station “cannot be restored.” Ukrhydroenergo also claimed Russia blew up the station from inside the engine room.

Ukraine and Russia have previously accused each other of attacking the dam.

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Blann reported from Kyiv. Associated Press writer Danica Kirka in London contributed.