As Russia continues to target and knock out electrical plants and distribution networks, "It's necessary for the whole country to prepare for electricity, water and heating outages," Kyrylo Tymoshenko, the deputy head of the Ukrainian president's office, told Ukrainian television.

Tymoshenko said there had been three Russian strikes on an unspecified energy facility. Kyiv mayor Vitali Klitschko said the attack was on "critical infrastructure" there, where Reuters witnesses saw thick smoke rising into the sky.

President Volodymyr Zelenskiy wrote on the Telegram messaging app "The terrorist state [Russia] will not change anything for itself with such actions. It will only confirm its destructive and murderous essence, for which it will certainly be held to account."

An air strike on the grid left the northern city of Zhytomyr without water and electricity supplies, its mayor said.

Zelensky earlier said the fresh wave of nationwide strikes -- which he said had damaged a residential buidling and flower market in Mykolaiv -- was a Russian attempt to "terrorize and kill civilians."

"The terrorist state will not change anything for itself with these kind of actions. It will only confirm its destructive and murderous essence, for which it will certainly be held to account," Zelensky said on social media.

There was no immediate reaction from Moscow.

Ukraine's state nuclear energy agency on Tuesday accused Russia of detaining two senior employees at the Russian-controlled Zaporizhzhia nuclear power plant in southern Ukraine.

Energoatom called on International Atomic Energy Agency (IAEA) chief Rafael Grossi "to make every effort" to secure their release.

Russian troops captured the Zaporizhzhia nuclear power plant at the beginning of March.

Meanwhile, President Vladimir Putin does not plan to end a military mobilization in Russia "yet. "Putin's spokesman Dmitry Peskov promised that authorities will not mobilize more people than Putin's set target of 300,000.

The mobilization has reportedly caused Russian men to be taken from the streets and conscripted, prompting a wave of hundreds of thousands of them to exit the country.

This report was prepared with information from Agence France-Presse and Reuters.