Russia was able to destroy a key power plant serving Kyiv because Ukraine ran out of defensive missiles, President Volodymyr Zelensky said Tuesday.

For three-and-a-half weeks, Russia has launched near continuous strikes on Ukraine's power grid, leaving over a million people without electricity.

The Trypilska thermal power station, one of the biggest electricity suppliers to the Kyiv region, was destroyed by Russian missiles on April 11.

"There were 11 missiles flying. We destroyed the first seven. Four destroyed Trypilska. Why? Because there were zero missiles," Zelensky said in an interview with US channel PBS.

"We ran out of missiles to defend Trypilska," he said.

Ukraine has grown increasingly frustrated at aid hold-ups from allies, including air defences which it says are urgently needed to repel deadly Russian attacks.

Zelensky's warning came as overnight storms put further strain on Ukraine's fragile energy system, cutting power to thousands of people.

"Due to the bad weather, 173 settlements in four regions are without power supply," Ukraine's energy ministry said Tuesday.

In the central region of Dnipropetrovsk, the worst affected area, over 15,000 people in 96 towns and villages were cut off, it said.

One of the main energy providers, DTEK, said its engineers had worked "all night and in the morning", adding: "We are making every effort to restore power to all homes by the end of the day".

National grid operator Ukrenergo warned earlier this month Ukraine's energy system needed an overhaul due to the repeated Russian attacks.