A senior Ukrainian energy official has warned that scheduled power outages and emergency blackouts will intensify over the coming weeks, after a string of Russian attacks crippled Ukrainian electricity generation.

President Volodymyr Zelensky said this month the aerial bombardments have halved the country's electricity production compared to a year ago, disrupting and limiting supplies for millions.

"Over the next few weeks, the situation will be much tougher than it is today," the head of national grid operator Ukrenergo, Volodymyr Kydrytsky said in an interview late on Sunday.

He said periods during which Ukrainians might not have power were likely to be extended by up to 12 hours per day and that outages could become more "stringent".

"This situation will continue until the end of July," he said in the interview, broadcast on state media.

In addition to systematic strikes on thermal and hydroelectric plants, he said there could be more outages due to maintainance work on nuclear plants and to weather conditions.

Scheduled outages could also be imposed during peak consumption periods and be "quite serious", Kydrytsky said.

Ukrainian officials have been forced to ramp up imports of electricity from neighbouring European Union countries to make up the shortfalls and have urged allies to help restoring the embattled energy sector.

Kyiv has also called on its allies to bolster Ukrainian air defence systems to safeguard critical infrastructure from Russian missile and drone barrages.