LONDON, Oct 1 (Reuters) - 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.As Russia confirmed the loss of its stronghold of Lyman in eastern Ukraine, Kadyrov slammed top commanders for their failings and wrote on Telegram: "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".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.After Russia's defeat in Kharkiv, Kadyrov said he would be "forced to go to the country's leadership to explain to them the situation on the ground" unless urgent changes were made in the conduct of the war."