Russia-Ukraine updates: Putin suspends key US-Russia nuclear treaty in speech denouncing West

U.S. Ambassador to the United Nations Linda Thomas-Greenfield traveled to Ukraine on Tuesday "to reiterate the United States' unwavering support as Ukraine defends its freedom and territorial integrity amidst Russia's brutal and unprovoked invasion," according to a statement from the U.S. Mission to the U.N.

While in the country's capital, Kyiv, Thomas-Greenfield "will meet with Ukrainian government leaders to discuss the ironclad American commitment to the sovereignty and independence of Ukraine," and she "will observe efforts to document and preserve evidence of atrocities committed by Russian forces and will hear first-hand accounts of survivors," according to the U.S. mission.

"Ambassador Thomas-Greenfield will also discuss the global food insecurity crisis exacerbated by Russia's invasion and will underscore the critical need for an extension of the Black Sea Grain Initiative into the coming year," the U.S. mission said. "She will also meet with humanitarian organizations working to meet winterization needs for vulnerable people impacted by Russia's attacks on energy and other civilian infrastructure."

President Joe Biden spoke to German Chancellor Olaf Scholz on Sunday and both agreed Russia's nuclear threats stemming the war in Ukraine are "irresponsible," according to the White House.

Both leaders said they would continue to "provide Ukraine with the economic, humanitarian, and security support it needs to defend against Russia," the White House said in a statement.

Biden and Scholz also spoke of the chancellor's recent trip to the People's Republic of China and, according to White House officials "affirmed their shared commitment to upholding the rules-based international order, human rights, and fair trade practices.”

-ABC News' Justin Gomez

The U.S. announced a new $400 million aid package for Ukraine that will help Kyiv procure tanks.

The aid money will go toward refurbishing 45 Soviet-era T-72 tanks belonging to the Czech Republic's defense industry, according to Pentagon spokesperson Sabrina Singh.

The Netherlands has also committed to paying for another 45 tanks to be refurbished for Ukraine.

The first of a total of 90 tanks is set to arrive before the end of the year, according to Singh.

"Since 2014, the US has committed more than $21 billion in security assistance and more than $18.2 billion since the beginning of Russia's unprovoked brutal invasion on Feb. 24," Singh said.

-ABC News' Matt Seyler

Western officials are "confident" Russia's military is "setting the conditions" for withdrawal from the Ukrainian city of Kherson, the only regional capital that has been occupied by Russian forces since the February.

The Russian military is preparing to make a "strategic" withdrawal and move its forces east across the Dnipro river, officials said.

"It looks like an orderly, well-planned and deliberate military process is taking place," a Western official told ABC News.

The officials would not put a timeframe on when the withdrawal would happen and added that it is not guaranteed to take place. They downplayed, however, any speculation that the Russians are using the withdrawal to mask a more "nefarious" action in that area.

The officials said their assessment was that the Russians believe Kherson "is not worth fighting for."

The advance of Ukrainian forces in Kherson has slowed over the past three weeks.

In mid-October, the newly appointed commander of Russian forces in Ukraine, General Surovikin, said “difficult decisions” may be necessary in Kherson.

Senior Ukrainian officials have suggested more recently that Russian forces are preparing to fight for Kherson and a source on the ground told ABC News that the Russian military is still moving in and out of the city.

-ABC News' Tom Burridge