Originally Published: 09 MAY 22 10:25 ET

Updated: 11 MAY 22 14:31 ET

By Kylie Atwood and Jennifer Hansler, CNN

(CNN) -- Vladimir Putin "has recognized he has no victory to celebrate," US Ambassador to the United Nations Linda Thomas-Greenfield told CNN in response to the lack of a major escalatory announcement in the Russian President's "Victory Day" speech Monday.

But the Russian leader also gave no indication that he plans to end the war in Ukraine, she cautioned.

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."

During a speech commemorating Russia's defeat of Nazi Germany at the end of World War II, Putin reiterated his baseless accusation that the West left him no choice but to invade Ukraine. Planned Victory Day air shows across Russia were canceled, raising questions as to why.

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.

'The conflict is not over'

Putin's speech provided little detail on how Russia plans to proceed in Ukraine. It followed days of speculation that the Russian leader would use the event to formally declare war on Ukraine, or order a mass mobilization of Russian forces to prosecute a war that has now stretched into its third month, with heavy Russian losses.

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.

The fact that Dvornikov oversaw Russia forces accused of committing atrocities in Syria and still remains in power to command forces accused of committing war crimes in Ukraine "is certainly something that the world has to address moving forward," Thomas-Greenfield acknowledged.

"We can't continue to allow individuals like this individual to carry out these acts and they absolutely can expect to be held accountable," she said, noting that the United States is working with Ukraine, the International Criminal Court, and the International Court of Justice "to ensure those responsible are held accountable."

'Demeanor changed significantly'

Thomas-Greenfield is among the Biden administration officials who has had the most interaction with Russia officials in the wake of the war given their seat on the UN Security Council.

She told CNN the behavior of the Russian diplomats she works with in New York has "absolutely" changed since Russia began its war in Ukraine, and that the seem "uncomfortable" in "the way they carry themselves, the demeanor."

She said she sees her Russian counterpart appear at the UN Security Council less frequently than before the war -- now he often sends his deputy or his experts in his place.

"From day one, the 24th of February, when we were sitting in an emergency meeting of Security Council and the Russians were president of the Security Council, we saw their demeanor changed significantly in the council," Thomas-Greenfield said, adding that she believes the Russians at the meeting "were taken by surprise by the attack" that evening that launched Russia's war in Ukraine.

Thomas-Greenfield said the Russian diplomats at the United Nations "certainly" are "reading off of prepared remarks."

"We know and expect when they will respond to things we say, but I suspect that everything is very much laid out for them and scripted," she said.

Thomas-Greenfield also told CNN her Ukrainian counterpart at the UN told her about Russians stealing grain from Ukraine, and although the United States has not confirmed the details, "there is some evidence that Russia, not only have they been attacking farmers' fields, they've been taking equipment, but also that they have removed grain from silos and taken that grain into Russia."

"I absolutely think it's credible," she said.

Concerns have loomed about the potential impact the war in Ukraine will have on its role as the "breadbasket of Europe." Multiple sources have told CNN that Russian forces are stealing farm equipment and thousands of tons of grain from Ukrainian farmers in areas they have occupied, as well as targeting food storage sites with artillery.

Ukraine's Defense Ministry said last week that an estimated 400,000 tons of grain had been stolen to date.