Russia's top security agency says it has arrested four Russians accused of making preparations to kill senior Defense Ministry officials on Ukraine's orders.

The Federal Security Service of Russia said a series of assassination attempts had been foiled. Four Russian citizens have been arrested.

Russia launched aerial attacks on Ukraine’s energy sector “on a massive scale” overnight into Wednesday, local authorities said, with explosions reported across the country amid intensified bombardments that have left Ukraine in a precarious position while the war grinds into a third winter.

Ukraine's air force says it detected 184 missiles and drones, causing damage to energy infrastructure across the country.

Moscow again struck Ukraine’s energy infrastructure, part of an effort to wear down the country. “In the trenches, there are no holidays,” one man said.

Finnish police are investigating whether a Russian ship was involved in the sabotage of an electricity cable running between Finland and Estonia. The authorities said on Thursday that they believe the anchor of the Eagle S, a tanker registered with the Cook Islands, may have damaged the Estlink 2 cable, which became disconnected on Wednesday.

Finnish authorities detained a ship linked to neighboring Russia as they investigate whether it damaged a Baltic Sea power cable and several data cables, police said, in the latest incident involving disruption of key infrastructure.

Damage to the power cable in the Baltic Sea is the latest in a spate of murky disruptions to undersea cables that have put European authorities on high alert.