Russia launched a major attack on Ukraine’s power grid on Saturday, cutting electricity to large parts of the country, Ukraine’s electricity operator said.

Ukrainian officials accuse Moscow of deliberately targeting energy infrastructure, causing repeated power outages and leaving thousands of people without heating as temperatures fall well below freezing.

Ukraine’s grid operator Ukrenergo said in a post on messaging app Telegram that “Russia is carrying out another large-scale attack on Ukraine’s power grid facilities.”

“Due to the damage inflicted by the enemy, emergency power outages have been implemented in most regions,” the company said.

It added that the attack was still ongoing and that repair work would begin “as soon as the security situation allows.”