In the first reaction from a Biden administration official to Putin's speech, Thomas-Greenfield noted to CNN that Putin did not use his remarks to announce a withdrawal from Ukraine -- which would have been welcomed by the United States -- which signals that Putin's war will continue.
"There was no reason for (Putin) to either declare victory or declare a war that he has already been carrying on for more than two months," Thomas-Greenfield said.
"His efforts in Ukraine have not succeeded," she added. "He was not able to go into Ukraine and bring them to their knees in a few days and have them surrender."
In a separate interview on CNN's "Connect the World" Monday, US Ambassador to NATO Julianne Smith said Putin's speech "wasn't that surprising" and "completely detached from reality."
"It's sad that on this day, on Victory Day, that he's celebrating aggression and oppression at the same time," she added.
Although Putin did not announce the speculated escalation plans, Thomas-Greenfield noted that the "the conflict is not over, for sure."
"He didn't announce a withdrawal. He didn't announce a deal with the Ukrainians," she told CNN. "So I suspect and we all assess that this could be a long-term conflict that could carry on for additional months."
Moreover, it would be too strong to say the United States "welcomed" Putin's remarks on Monday, Thomas-Greenfield told CNN, because the "unconscionable war on the Ukrainian people" continues.
"So what we would see as a positive sign is for Putin to pull his troops out of Ukraine and bring this unconscionable war to an end," she said.
Thomas-Greenfield, who was in Brussels for a major conference to support Syria, said Moscow's appointment of the "Butcher of Syria" Alexander Dvornikov to command Russia's offensive in Ukraine is "just another example of Russian brutality, Russia's lack of consciousness about humanity, the human rights violations and atrocities that they have committed and they are prepared to continue to carry out in Ukraine."
"It just shows to the world that there are no limits, as far as the Russians are concerned, to their willingness to use every single tool to bring the Ukrainian people down," she told CNN.