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.

President Biden on Wednesday denounced Russia’s latest attack on Ukraine, declaring the wave of missiles and drones “outrageous.” “The purpose of this outrageous attack was to cut off the Ukrainian people’s access to heat and electricity during winter and to jeopardize the safety of its grid,

The flight was en route from the Azerbaijani capital of Baku to Grozny, in Russia’s south, when it diverted and attempted an emergency landing in Kazakhstan.

Officials in Russia and Kazakhstan are urging people to wait for an investigation into the deadly Azerbaijan Airlines plane crash before assigning blame.

"No one claims that it was done on purpose," an Azerbaijan official told Reuters. They added their government "expects the Russian side to confess."