Strikes that have left millions without electricity and water at the start of winter but the Russian military has said the campaign is part of its military plan. "There's a lot of noise about our strikes on the energy infrastructure of a neighbouring country. Yes, we do that. But who started it?" Mr Putin said at an awards ceremony in the Kremlin, adding that the criticism would "not interfere with our combat missions."
He presented the strikes as a response to a blast on Moscow's bridge to annexed Crimea and other attacks, accusing Kyiv of blowing up power lines from the Kursk nuclear power plant and not supplying water to Donetsk in eastern Ukraine.
"Not supplying water to a city of more than a million people is an act of genocide," Mr Putin said.
A Kremlin spokesman said the threat to Crimea was rising. "There are certainly risks because the Ukrainian side continues its policy of organising terrorist attacks. But, on the other hand, information we get indicates that effective countermeasures are being taken," Kremlin spokesman Dmitry Peskov said.
The Russia leader on Wednesday said nuclear tension had risen because of the war as he gave no sign of any intent to let up in the battle.
“Of course, it might be a lengthy process,” he told a meeting of the Kremlin's human rights council.
Ukrainian President Volodymyr Zelenskyy — who was declared Time magazine's “Person of the Year” on Wednesday for his “defence of freedom” — said six people were killed in the latest Russian strikes, this time on a village in the frontline region of Donetsk.
That came a day after Ukrainian artillery strikes killed six people in the Russian-occupied regional capital city of Donetsk, local officials said.
Ukraine war latest — in pictures
In the Kremlin meeting, Mr Putin appeared to caution against expectations of any early resolution to the conflict, repeating that it would be a long process.
But he sparked fresh concerns in the West as he broached anew the issue of whether the war could escalate to the use of nuclear weapons.
Mr Putin, who has previously hinted at the possibility of the use of small tactical weapons in the war, remained evasive on his intentions.
“Such a threat is rising. Why make a secret out of it here?” he asked.
“Russia will under no circumstances use them first.
“But if it does not use them first under any circumstances, then it will not be the second to use them either, because the possibilities of using them in the event of a nuclear strike against our territory are very limited.”
Putin's inner circle — in pictures
US State Department spokesman Ned Price condemned the nuclear talk, as vague as it was.
“We think any loose talk of nuclear weapons is absolutely irresponsible,” Mr Price told reporters.
“It is dangerous, and it goes against the spirit of that statement that has been at the core of the nuclear non-proliferation regime since the Cold War.”
After more than nine months of war, Russian forces have missed most of their key military goals, including toppling the Ukrainian government and completely capturing the Donbas region.
Vladimir Putin annexes four regions of Ukraine — in pictures
Nevertheless, Mr Putin told the meeting that the Ukraine lands that Russian forces have occupied and declared annexed were a “significant result” of the military campaign.
He made special reference to Russia's control now of all the land along the Azov Sea.
“The Azov Sea has become an internal sea to the Russian Federation — that's a serious thing,” he noted.
But he promised there would not be a new wave of mobilisation, amid domestic Russian fears of a new call-up. Western officials say Russian troops have taken heavy personnel and equipment losses in recent fighting.
“Out of 300,000 of our mobilised fighters, our men, defenders of the fatherland, 150,000 are in the area of operations”, including 77,000 in combat units, he said.