Ukraine's energy minister said on Monday the damage from a major Russian attack on the country's energy facilities is likely to run into the "billions".

Russia last week mounted what Kyiv says was its largest ever overnight aerial bombardment -- firing around 90 missiles and 60 drones at energy facilities across the country and killing at least five people.

"We need more time (to assess the damage) because there are large amounts of debris," Ukrainian Energy Minster German Gerashchenko told journalists on Monday.

In terms of the cost of repairs, "the real figures will be after assessment of the damage but I think it is in the region of billions, for sure," he said.

Gerashenko did not specify what currency he was referring to.

The World Bank has estimated the total cost of reconstruction facing Ukraine more than two years since the start of the war is at least $486 billion.

Gerashchenko called the strikes the "biggest attack since the beginning of the full-scale invasion" in February 2022.

Among facilities hit were power stations that had been recently renovated, he said.

"They continue these attacks every day," he said on Monday, pointing to an overnight Russian attack on the southern city of Odesa.

Power was cut off to part of the Black Sea port city when debris from a shot-down drone hit an energy plant.

Ukraine's second largest city of Kharkiv is currently experiencing "the most difficult situation", he said.

A missile attack completely cut off power to the eastern city last Thursday, also knocking out water and heating supplies to hundreds of thousands of homes.

  'Weaponising the energy sector' 

 Critical infrastructure was being provided with power now, though some supplies to households were still restricted, he said.

On Monday, Gerashchenko met Sweden's minister for energy, business and industry, Ebba Busch, who was making her first official visit to Ukraine.

Busch condemned the latest attacks and said Russia was "weaponising the energy sector".

The ministers held a press conference in the cellar of a government building in central Kyiv after Russia fired ballistic missiles at the capital.

Loud explosions were heard and air raid sirens rang out on Monday morning.

Gerashchenko said the only way to protect the country's electricity network fully was through better air defences.

"The efficiency of air defences -- that is the answer," he said.

"(A) "modern system like Patriot could easily shoot down the ballistic missile -- so it means that we need more."

Ukraine is now importing electricity from other countries to keep the lights on.

Gerashchenko said the country needs to be able to import more electricity from the European Union than its current capacity of 1.7 gigawatts.

"We need more. Today, unfortunately, this is a question of survival."