Ramzan Kadyrov, head of Russia's region of Chechnya, said on Saturday that Moscow should consider using a low-yield nuclear weapon in Ukraine after a major new defeat on the battlefield.
In a message on Telegram addressing Russia's loss of its stronghold of Lyman in eastern Ukraine, Kadyrov wrote: "In my personal opinion, more drastic measures should be taken, right up to the declaration of martial law in the border areas and the use of low-yield nuclear weapons".
He was speaking a day after President Vladimir Putin proclaimed the annexation of four Ukrainian regions - including Donetsk, where Lyman is located - and placed them under Russia's nuclear umbrella, saying Moscow would defend the lands it had seized "with all our strength and all our means".
Russia has the world's largest atomic arsenal, including low-yield tactical nuclear weapons that are designed to be deployed against opposing armies.
Other top Putin allies, including former president Dmitry Medvedev, have suggested that Russia may need to resort to nuclear weapons, but Kadyrov's call was the most urgent and explicit.
The influential ruler of the Caucasus region of Chechnya has been a vocal champion of the war in Ukraine, with Chechen forces forming part of the vanguard of the Russian army in Ukraine.
In his message, he slammed Colonel-General Alexander Lapin, commander of the Russian forces fighting at Lyman, calling him "a mediocrity".