Russian President Vladimir Putin has warned the threat of nuclear war is increasing as he boasted his country has the world’s most advanced nuclear weapons.

In his latest chilling comments, Mr Putin added that Russia would strike back if hit.

But he hoped that its arsenal would be a deterrent and he assured that “we are not going to brandish these weapons like a razor, running around the world”.

“We have not gone crazy,” he told a meeting at the Kremlin.

“We are aware of what nuclear weapons are. We have these means, they are in a more advanced and modern form than those of any other nuclear country, this is obvious.”

Mr Putin was speaking to Russia’s Human Rights Council.

“In terms of the threat of nuclear war, you are right, such threat is increasing,” he said.

“As for the idea that Russia wouldn’t use such weapons first under any circumstances, then it means we wouldn’t be able to be the second to use them either – because the possibility to do so in case of an attack on our territory would be very limited.”

Mr Putin said Russia had a strategy “namely, as a defence”.

“We consider weapons of mass destruction, nuclear weapons – it is all based around the so-called retaliatory strike – that is, when we are struck, we strike in response.”

He said: “This is a deterrent factor that does not provoke the expansion of conflicts, but a deterrent, and I hope everyone understands this.”

The long war

Mr Putin has also acknowledged his invasion of Ukraine is taking longer than expected and his army could be fighting for a long time.

In a televised meeting with loyalists on Wednesday, he said, “This can be a long process.”

About 150,000 of the 300,000 reservists called up in September and October were deployed in Ukraine, 77,000 in combat units, he said.

The remaining 150,000 were still at training centres.

Despite recent retreats on the battlefield, including the loss of Kherson, the one Ukrainian provincial capital Russia captured, Mr Putin has said he has no regrets about launching a war that is Europe’s most devastating since World War II.

He said Russia had already achieved a “significant result” with the acquisition of “new territories”, a reference to the annexation of four partly occupied regions in September that Ukraine and most members of the United Nations condemned as illegal.

Russian forces have fired more than 1000 rockets and missiles at Ukraine’s power grid, which is still working despite taking major damage, Interfax Ukraine news agency reported, citing Volodymyr Kudrytsky, chief executive of the Ukrenergo grid operator.

Eight recent waves of Russian air strikes have seriously damaged the grid and led to emergency and planned outages across the country, including in the capital Kyiv, a city of three million.

Kyiv Mayor Vitali Klitschko warned of an “apocalypse” scenario without power, running water or heat this winter if Russian air strikes on infrastructure continue. He said there was no need for residents to evacuate now, though they should be ready to do so.

Kyiv could be left without central heating at a time when temperatures could fall as low as -15 degrees, Mr Klitschko told Reuters.