A former US army commanding general says efforts to stop Russia's invasion can no longer be deterred by "exaggerated fears" of nuclear repercussions.
Two top officials of the Biden administration have pledged more than $700 million in aid to Ukraine and other countries in the regions.
Secretary of State Antony Blinken and Defence Secretary Lloyd Austin had a face-to-face meeting with President Volodymyr Zelensky on Monday.
Austin said he wanted to see Russia weakened.
Former commanding general of US Army Europe Ben Hodges told Morning Report the visit represented a "huge" moment in determining the tide of the conflict.
Hodges said the visit made it clear that the US was making a concerted effort to help Ukraine win the war.
"It will drag on if we don't act decisively, if we do what Secretary Austin just talked about - getting the Ukrainians everything that they need so they can win - then this will be over in a few months," he said.
US Secretary of State Antony Blinken signalled an intention to restore diplomatic operations in Ukraine with a candidate for the ambassador role already nominated.
Hodges said the decision to reinstate diplomatic services in Ukraine was as important as the choice to provide weapons.
He said there would be three key elements to any outcome that would be considered a "win" for the US.
"Number one at a minimum [pushing] Russia back to the pre-24 February line so not one inch of Ukraine remains under their control that they took when they attacked," Hodges said
Secondly, he said the US was committed to the long term reinstatement of Ukraine's sovereignty including the return of both the Crimea and Donbas regions.
"The third piece is all these tens of thousands of Ukrainians that have been kidnapped or deported, bring them back to their homes."
He said Russia's historical actions meant the prospect of reaching a settlement offered little assurance Putin's regime would stop military action in Ukraine.
Hodges said the US had been deterred for several weeks by "exaggerated fears" of Russia's nuclear capabilities.
"Of course there is some risk and there's no doubt Russia has thousands of nuclear weapons they could use them but I honestly think this is very unlikely.
"Eight weeks ago, we were arguing over whether or not to give [Ukraine] stingers, now we've finally reached the point of five battalions worth of howitzers and 180,000 rounds and all these other things are coming and Russia has not done anything else except shake their fist."
He said utilising nuclear weapons offered Russia no battlefield advantage and would force western military forces into action.