The capital Kyiv and Ukraine's second biggest city, Kharkiv, came under fire in overnight air strikes that Ukraine's energy minister said were spread across eight regions and followed a brief moratorium on attacks on energy facilities.
Russia launched 450 drones and over 70 missiles and at least nine people were wounded in attacks that struck apartment blocks as well as energy infrastructure, Ukrainian officials said.
At least 10 people were wounded, officials said.
Electricity and heating was knocked out in many areas, with temperatures around or below -20C.
"Taking advantage of the coldest days of winter to terrorise people is more important to Russia than resorting to diplomacy," Ukrainian President Volodymyr Zelenskiy wrote on Telegram, accusing Moscow of choosing "terror and escalation".
He was referring to talks involving Russian, Ukrainian and US officials scheduled to be held in Abu Dhabi on Wednesday and Thursday as Washington tries to broker an end to nearly four years of war since Russia invaded Ukraine in February 2022.
The first round of trilateral talks in late January led to no movement on the vital question of territory, with Moscow demanding Kyiv cede more land in east Ukraine, which it refuses to do.
Zelenskiy has said Ukraine, which is struggling to stop grinding Russian advances on the battlefield, was ready for "substantive" talks. Moscow and Kyiv blame each other for the failure to agree a peace deal.
Kyiv is under US pressure to agree to a peace deal while attacks by Russia on Ukraine's energy system appear intended to freeze it into submission during one of the coldest winters in years.
Russia and Ukraine said last week they had halted strikes on each other's energy infrastructure, but they disagreed on the time frame for the moratorium and there were again widespread attacks on Ukrainian energy facilities overnight.
Among the infrastructure that was hit overnight were facilities to heat water for distribution to Ukrainian homes.
Earlier, Ukraine agreed with Western partners that any persistent Russian violations of a future ceasefire agreement would trigger a co-ordinated military response from Europe and the US, the Financial Times reports, citing people briefed on the discussions.
Reuters could not immediately verify the report.
The plan was discussed on several occasions in December and January between Ukrainian, European and American officials and would involve a multi-tiered response to any breaches of an agreed armistice by Russia, the report said.
The report emerged ahead officials from Kyiv, Moscow and US special envoy Steve Witkoff meeting in Abu Dhabi on Wednesday and Thursday for talks aimed at ending the war.
As per the proposal, any Russian breach of a ceasefire would prompt a response within 24 hours, starting with a diplomatic warning and, if necessary, action by Ukrainian army to halt the infraction, the FT said.
If hostilities continued beyond that, the proposal would move to a second phase of intervention using forces from the so-called coalition of the willing, which includes many EU members and the UK, Norway, Iceland and Turkey, the report said.
The report added that in the case of an expanded attack, a co-ordinated response by a Western-backed force, incorporating the US military would be triggered 72 hours after the initial breach.
Ahead of the Abu Dhabi talks, Zelenskiy was optimistic about achieving a dignified and lasting peace.
"We consider the bilateral security guarantees document with the United States to be complete, and we anticipate further substantive work on documents related to recovery and economic development," he said.
with agencies
