Russia has launched its "most powerful blow" against Ukraine's energy sector so far this year, according to the private energy company, DTEK.

The combined missile and drone strikes which targeted power plants and infrastructure in Kyiv and multiple locations left the system operating with "serious restrictions", it said.

The strikes were launched as temperatures dropped to -20C (-4F) and left more than 1,000 tower blocks in the capital without heating once again and damaged a power plant in the eastern city of Kharkiv beyond repair.

President Volodymyr Zelensky said Russia was "choosing terror and escalation" rather than diplomacy to end this war and called for "maximum pressure" on Moscow from Ukraine's allies.

The attack comes after a so-called "energy truce" agreed by Donald Trump with Vladimir Putin expired at the weekend.

It also came on the day Nato Secretary-General Mark Rutte was in Kyiv to meet President Zelensky and to address the national parliament.

Donald Trump's initiative was meant to give diplomacy a chance. Negotiators from Russia and Ukraine are due to meet in Abu Dhabi for another round of talks co-ordinated by the US later this week.

It is clear that Russia has other ideas.

And in fact, there is always a gap between Russia's massive strikes which makes Ukrainians doubt there was ever any real pause at all.

We heard the first explosions in Kyiv soon after midnight and the air raid lasted more than seven hours. There were several subsequent blasts.

Residents spent the night sheltering in metro stations, with some pitching tents on the platforms to protect them from the freezing cold.

President Zelensky has said more than 70 ballistic and cruise missiles were fired - significantly more than usual - together with 450 drones which are used to overwhelm Ukraine's air defences.

Ukraine's Air Force said it had intercepted only 38 of the missiles, which means many reached their target.

Officials here have complained repeatedly of a shortage of missiles to protect the skies. Ukraine relies on US-made Patriot missiles, in particular.

"Timely delivery of missiles for air defense systems and the protection of normal life are our priority," Zelenksy wrote on X this morning. "Without pressure on Russia, there will be no end to this war."

Volodymyr Zelensky has accused Moscow of using the coldest days of winter to "terrorise people".

DTEK has confirmed that two of its own power plants were hit again overnight, including in Odesa, in what it says was the ninth massive attack on the sector since October.

State-run facilities were hit in Kyiv, Dnipro and elsewhere, adding to serious damage caused by a series of previous targeted attacks.

DTEK says some of the plants targeted were providing heating only, not electricity, which means they were exclusively for civilian use. The Geneva Convention makes clear that targeting civilian infrastructure is a potential war crime.

Each time makes it harder to carry out repairs and leaves the system more fragile, and prone to blackouts.

Teams of engineers have been working through the night for weeks to fix things - drafted in from all over the country and hailed as heroes.

But there are not enough workers to keep up with demand.

We have met residents who have had no heating in their homes for days, in some cases weeks. They sleep in hats and coats, and under piles of blankets, but it is still bitterly cold.

Many use soup kitchens to get free hot meals because there are also power cuts here for hours on end.

People believe these attacks are intended to turn them against the authorities in Kyiv, to make their lives so miserable they submit to Russia's demands - including to hand over land in the eastern Donbas region that Moscow currently does not control.

Instead, there is a lot of anger here at Russia for attempting to freeze civilians in their homes as well as resistance to any form of compromise with Moscow.

"Russia won't get what it wants," Vera told the BBC this weekend, as she queued for a bowl of stew served by volunteers. "We are stronger than them in any case."

Volodymyr said he planned to sleep in a local school for a few days, which has a generator to keep it warm. "In the daytime you move around a bit," he said. "But at night it's really cold."

He was furious with Russia. "They are bombing civilians. They want us to freeze and die," he said.

Several residential buildings were damaged in the latest attack and set on fire by falling debris as Ukraine shot down missiles and drones. Several people were injured.