A series of large explosions rocked the town of Nova Kakhovka in the Kherson region of Ukraine on Monday night. The town, like much of Kherson, is under Russian occupation. 

It's the second major explosion in four days in the town, the site of an important hydro-electric dam and a link in the water supply to Crimea through the North Crimea canal.

Video posted on social media showed loud explosions and a huge ball of fire lighting up the night sky.

Serhiy Khlan, a Ukrainian official who is a member of Kherson regional council, said on Facebook: "In Nova Kakhovka minus one Russian ammo depot. They brought, brought, stockpiled, stockpiled and now have fireworks at night."

Khlan, who is not in Kherson, warned residents of Nova Kakhovka not to venture outdoors. 

"Please take care of yourself and do not come close to the place of the detonation," he said.

The Russian state news agency TASS made no reference to an ammunition dump exploding but late Wednesday reported: "The Armed Forces of Ukraine attacked the Kakhovka hydroelectric power station in the Kherson region, a source said."

But the deputy head of the Russian backed military-civilian administration in Kherson, Kirill Stremousov, said that Ukrainian missiles did not hit the hydroelectric power station.

TASS later said that warehouses holding potassium nitrate had exploded. Potassium nitrate is a highly combustible substance used as an ingredient in fertilizer and was the cause of the Beirut explosion two years ago.

CNN cannot confirm the cause of the explosions or what was destroyed. TASS reported: "There are victims, the market, hospital and houses were damaged," quoting the Russian-backed civil-military administration in Kherson.

Ukrainian forces have stepped up attacks using missiles and long range artillery against Russian command posts and munitions sites in the last week.