Russia's rhetoric on the subject of nuclear arms has been "reckless" ever since it invaded Ukraine in February 2022, Press Secretary Karine Jean-Pierre said.

"We have not seen any reasons to adjust our own nuclear posture, nor any indication that Russia is preparing to use a nuclear weapon in Ukraine," Jean-Pierre said when asked about Putin's comments.

Putin appeared to be "restating Russia's nuclear doctrine" after he was asked during an interview about using the weapons, Jean-Pierre told reporters traveling with Biden on a campaign trip to Milwaukee.

"Nevertheless, Russia's nuclear rhetoric has been reckless and irresponsible throughout this conflict," she added.

"It was Russia that brutally invaded Ukraine without provocation or justification, and we'll continue to support Ukraine as they defend their people and their territory from Russian aggression."

Putin on Wednesday lauded Moscow's nuclear arsenal and warned that he was ready to deploy the weapons if Russia's sovereignty was under threat.

The Kremlin has touted its nuclear prowess throughout its two-year offensive in Ukraine. Putin's latest comments come days ahead of elections in Russia that look set to hand him another six years in power.

Biden on Tuesday announced a $300 million emergency weapons package to prop up Ukraine after recent Russian gains, while the US Congress blocks further aid.