KYIV, Ukraine (AP) — Ukraine on Tuesday accused Russian forces of blowing up a major dam and hydroelectric power station in a part of southern Ukraine they control, threatening a massive flood that could displace hundreds of thousands of people, and ordered residents downriver to evacuate.

Russian news agency Tass quoted an unspecified Russian government official as saying the dam had “collapsed” due to damage.

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 hundreds of thousands of people live.

President Volodymyr Zelenskyy called an emergency meeting to deal with the crisis.

The nearby Russian-occupied Zaporizhzhia nuclear power plant could also be affected. Its cooling systems are supplied with water from the Kakhovka reservoir, held up by the dam. The International Atomic Energy Association wrote on Twitter that there was “no immediate nuclear safety risk at (the) plant.”

The Ukrainian Interior Ministry wrote on Telegram that the Kakhovka dam had been blown up, and called for residents of 10 villages on the river’s right bank and parts of the city of Kherson downriver to gather essential documents and pets, turn off appliances, and leave, while cautioning against possible disinformation.

Footage from what appeared to be a monitoring camera overlooking the dam that was circulating on social media purported to show a flash, explosion and breakage of the dam.

Oleksandr Prokudin, the head of the Kherson Regional Military Administration, said in a video posted to Telegram shortly before 7 a.m. that “the Russian army has committed yet another act of terror,” and warned that water will reach “critical levels” within five hours.

Zelenskyy moved to convene an emergency meeting of the country’s security and defense council following the dam explosion, the council’s secretary, Oleksiy Danilov, wrote on Twitter.

Ukraine and Russia have previously accused each other of targeting the dam with attacks, and last October Zelenskyy predicted that Russia would destroy the dam in order to cause a flood.

Authorities, experts and residents have for months expressed concerns about water flows through — and over — the Kakhovka dam.

By mid-May, after heavy rains and snow melt, water levels rose beyond normal levels, flooding nearby villages. Satellite images showed water washing over damaged sluice gates.

Ukraine controls five of the six dams along the Dnipro River, which runs from its northern border with Belarus down to the Black Sea and is crucial for the entire country’s drinking water and power supply. The Kakhovka dam — the one furthest downstream in the Kherson region — is controlled by Russian forces.