John Bolton, a former US national security adviser and ambassador to the United Nations, said that the Russian president is in “greater trouble than at any point since the invasion,” Report informs, citing Sky News.

Vladimir Putin’s mounting problems in Ukraine make Russia’s use of a tactical nuclear weapon more likely, a senior US expert has told Sky News.

When asked what the US response might be, Mr Bolton said: “I don’t think it needs to be nuclear, depending on what the Russians actually do.

“But I do think we should say it would be Vladimir Putin signing a suicide note if he authorised even a tactical nuclear weapon.

“It’s very important that we deter the use of a nuclear weapon.