KYIV, June 6 - A major dam in southern Ukraine collapsed Tuesday, flooding villages, endangering crops 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, which sits on the Dnipro River in an area Moscow has controlled for more than a year.

President Volodymyr Zelenskyy called it “the largest man-made environmental disaster in Europe in decades.” U.N. Secretary-General Antonio Guterres called it “another devastating consequence of the Russian invasion of Ukraine.”

As homes, streets and businesses flooded, authorities expressed concerns about drinking water supplies and emergency crews evacuated thousands of people from Ukrainian and Russian-controlled areas.

Both Russian and Ukrainian authorities brought in trains and buses to move residents to safety. About 25,000 people in Russian-controlled areas and 17,000 in Ukrainian-held territory should be evacuated, Ukraine’s deputy chief prosecutor Viktoriia Lytvynova said on Ukrainian television. Neither side reported any deaths or injuries.

A satellite photo Tuesday morning by Planet Labs PBC analyzed by The Associated Press showed more than 600 meters (over 1,900 feet) missing from the wall of the 1950s-era dam.

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.

Zelenskyy told reporters his government knew last year that Russia had mined the dam, so “there may come a moment when an explosion occurs.” Other Ukrainian officials alleged Russia blew up the dam to hinder Kyiv’s counteroffensive, even though observers note that crossing the broad Dnieper would be extremely challenging. Other sectors of the front line are more likely avenues of attack, analysts say.

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

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 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 been concerned for months about water flowing through — and over — the Kakhovka dam. After heavy rains and snowmelt last month, water levels rose beyond normal, flooding nearby villages. Satellite images showed water washing over damaged sluice gates.

Zelenskyy alleged Russian forces set off a blast inside the dam structure at 2:50 a.m. local time and said about 80 settlements were in danger.

White House National Security Council spokesman John Kirby told reporters the U.S. “cannot say conclusively what happened” and declined to assess the impact on Ukraine’s counteroffensive.

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

U.N. humanitarian chief Martin Griffiths told the Security Council that at least 40 settlements in the Kherson region were already flooded.

The Russia-installed mayor of Nova Kakhovka, which had a prewar population of about 45,000, said the city was being evacuated. (ap/ez)