Dmitry Medvedev, the deputy chairman of Russia's Security Council, said that Russia has not yet used the full arsenal of weapons at its disposal in its war with Ukraine.
The comments on Telegram did not specify what weapons he meant. But it appeared to be a reference to Russia's vast nuclear arsenal, which officials have gestured towards but not deployed in the conflict.
Medvedev has made previous nuclear threats against Ukraine, remarking in September that to Russia has the right to defend itself with nuclear weapons if it is pushed beyond its limits and that this is "certainly not a bluff".
His boss, Russian President Vladimir Putin, has similarly spoken of situations in which Russian could use nuclear force, though experts told Insider in October that scenario was still unlikely.
Medvedev wrote in his latest message: "Russia, for obvious reasons, has not yet used its entire arsenal of possible weapons, equipment and munitions. And did not attack all possible enemy targets located in populated areas."
"And not only from our inherent human kindness. Everything has its time."
His comments came after Russia announced abandoned the Ukrainian city of Kherson, the greatest in a series of recent defeats for Russia in its faltering invasion of Ukraine.
Civilians were seen embracing Ukrainian soldiers as they entered the city Sunday, and the country's president Volodymyr Zelenskyy made a surprise visit to the city Monday. Ukraine has pushed back Russian forces across a large swath of east Ukraine.
Medvedev previously served as Russia's president, whe he presented himself as a liberalizing reformer. But in recent years he has stood out as one of the most aggressive figures in the Russian elite.
He has made a series of threats Ukraine on social media, and has pushed rhetoric about Ukraine which human-rights experts say constitutes an incitement to genocide.
US National Security Advisor Jake Sullivan said last month the consequences of using nuclear weapons for Russia would be "catastrophic."
Military analysts say that Russia has been badly depleted of manpower and equipment by the war. Thousands of civilians have been drafted into the military and sent into combat with rudimentary weapons and training, according to Western intelligence assessments.