KYIV, Ukraine -  Ukraine warned Friday that Russian air attacks were putting its electricity supply under "increasing threat", hours after strikes damaged power stations and killed at least one person.

Moscow has stepped up aerial bombardment of Ukraine in recent weeks, targeting energy infrastructure in response to deadly Ukrainian assaults on Russia's border regions.

A Russian drone killed a 39-year-old man and wounded another person near the southeastern city of Nikopol, while an air attack on Kamianske further north wounded five people, including a child, authorities said.

"Last night Russia continued its barbaric attacks against the Ukrainian energy system. Emergency blackouts have been introduced in some regions," Prime Minister Denys Shmygal said.

He said the strikes showed Ukraine urgently needed more air defence systems, a demand Kyiv has repeatedly made to its Western allies as its energy sector buckles under pressure.

"Enemy attacks are becoming more frequent and massive, posing an increasing threat to Ukraine's energy security," Ukraine's foreign ministry said.

- 'Use electricity sparingly' -

Russia has battered Ukrainian energy infrastructure throughout the two-year war, in attacks that President Volodymyr Zelensky has called "energy terrorism" and that the United Nations has described as illegal.

The air force said Moscow had targeted Ukraine's "fuel and energy sector" with 99 missiles and drones overnight, 84 of which were shot down.

"Russian missiles hit thermal and hydroelectric power plants," national grid operator Ukrenergo said in a statement.

"Currently, restrictions are in place in the regions of Kryvyi Rig and Kharkiv. In the evening, restrictions are possible in the eastern and Dnipro regions," it said.

"Please use electricity sparingly," the company added.

One of the country's main energy providers, DTEK, said three thermal power stations had been attacked in the barrage, leaving facilities "severely damaged".

"After the attack, the power engineers promptly started to deal with the consequences," the company said in a statement online, adding that one employee had been wounded.

The energy ministry said the attack damaged power infrastructure in four regions across central and western Ukraine, causing blackouts and disrupting train traffic.

On the frontlines, Ukraine has been forced onto a defensive footing in the past few months as it struggles with ammunition shortages amid delays to a $60 billion aid package from Washington.

Its armed forces commander Oleksandr Syrsky said Friday the situation in some areas of the battlefield was "tense".

"The Russian occupiers continue to increase their efforts and have a numerical advantage in personnel," he said.

"In addition, the enemy is conducting heavy artillery and mortar fire," he added.

"Just a few days ago, the enemy's advantage in terms of ammunition fired was about six to one."