More than 80 Russian missiles hit Ukraine, killing 6

More than 80 Russian missiles were fired across Ukraine on Thursday, leaving six people dead and hundreds of thousands without electricity or heat.

The attack, which is the largest in three weeks, also put the Zaporizhzhia nuclear power plant at risk of meltdown, as it was knocked off the power grid and was unable to run the necessary cooling systems for several hours before being reconnected, according to The Associated Press.

Russia also launched eight exploding Iranian-made Shahed drones in its latest barrage, Valerii Zaluzhnyi, the chief commander of Ukraine's armed forces, said. 

Rafael Mariano Grossi, who leads the U.N.'s nuclear watchdog agency, raised concerns Thursday about nuclear safety after the attack. 

"Each time we are rolling a dice," he said at an International Atomic Energy Agency meeting. "And if we allow this to continue time after time, then one day our luck will run out."

Russia has been targeting Ukrainian utilities since October.