Russian Deputy Foreign Minister Sergey Ryabkov warned Tuesday that the United States should stop supplying Ukraine with weapons and making threats to Moscow in order to "preserve relations" with Russia.

"They simply need to stop in their escalation, both verbal escalation and in terms of stuffing the Kyiv region with weapons. They need to stop producing threats to Russia," Ryabkov said while answering questions from reporters in Moscow. "Meanwhile, if they do manage to somehow positively influence Kyiv, something that I not just doubt, but I am confident that it will not happen, unfortunately, then I think there will be a certain prospect for normalizing relations."

"For now, we see a downward tendency in relations with our country through the fault of the U.S.," he added. "We regret it, but it does not impact our determination to move toward accomplishing the goals of the special military operation and to adapt to the circumstances related to the American sanctions and the sanctions imposed by European satellites of the U.S. at its behest."

When asked whether Moscow plans to recall its ambassador, Ryabkov told reporters that the future of Russia-U.S. relations depends on Washington.

"A note of protest was passed to the American ambassador yesterday. It said that the current developments put these relations on the brink of a breakup," he said. "There is nothing here beyond what was said there: that the question is about a policy that the U.S. will choose."

U.S. President Joe Biden said Russia has used a hypersonic missile in Ukraine, explaining Monday night that it's "the only thing that they can get through with absolute certainty."

"It's a consequential weapon," Biden said during remarks at the Business Roundtable's CEO Quarterly Meeting in Washington, D.C. "It doesn't make that much difference except it's almost impossible to stop it. There's a reason they're using it."

Biden warned that "the more [Putin's] back is against the wall, the greater the severity of the tactics he may employ," and started to describe false flag operations by Russia, specifically its false claims that the United States and Ukraine are developing chemical or biological weapons for use against Russia.

He said those claims are a "clear sign" he's considering using those types of deadly weapons.

"He's already used chemical weapons in the past, and we should be careful of what - what's about to come," Biden said. "He knows there'll be severe consequences because of the United NATO front, but the point is, it's real."

-ABC News' Justin Gomez

Ukrainian President Volodymyr Zelenskyy acknowledged the Ukrainians defending their country in his address Monday, in which he described the Russian forces as "slaves" whose consciousness has been replaced by propaganda.

Zelenskyy called out to Ukrainians in several cities, including those trapped in the besieged city of Mariupol, telling them, "Never think even for a moment that Ukraine does not remember you."

The Ukrainian president also acknowledged the "heroes emerging among the millions" as Ukrainians continue to take up arms against the invaders.

"Once, ordinary Ukrainians, and now, fighters," Zelenskyy said. "Men and women who stand up for our state. Everywhere — in the south, in the east, in the north, in the center, in the west and abroad."

Zelenskyy urged the public to continue to stand up so the "enemy does not believe that this is a reality."

"We will make them remember that they are not welcome," he said.

-ABC News' Christine Theodorou

Russian forces have "failed to achieve a lot of their objectives on the ground" due to heavy Ukrainian resistance, Pentagon spokesman John Kirby said Monday.

"When you look at what they've managed to do in 26 days, it's not that impressive," Kirby said during a press briefing. "I think what we're seeing here is the Russians have been flummoxed, they've been frustrated, they have failed to achieve a lot of their objectives on the ground."

Kirby declined to say whether Russia’s operations had entered a "new phase" as they shift to launching artillery and missile attacks on Ukraine’s cities but said that they are stepping up their long-range bombardment "because they are essentially still stalled."

"They're lobbing an awful lot of hardware into the cities to try to force their surrender, and it’s increased over the last few days," he said, adding that the tactic has led to more civilian casualties and damage to civilian areas.

-ABC News' Luis Martinez

All Russian troops have left the Ukrainian cities of Kyiv and Chernihiv, withdrawing north toward the borders of Belarus and Russia to consolidate before likely redeploying to the Donbas region in eastern Ukraine, a senior U.S. defense official told reporters Wednesday.

But even with the Russians gone, the territory remains treacherous.

"There are some indications that they left behind mines and things like that, so the Ukrainians are being somewhat careful in some areas north of Kyiv as they begin to clear the ground and clear the territory and re-occupy it," the official said.

While the U.S. hasn't yet seen these troops redeploy elsewhere in Ukraine, it'll likely happen soon, according to the official. Ukrainian forces are preparing for a major fight in Donbas, the official said.

The official also said the Pentagon is "monitoring" an apparent nitric acid explosion in Ukraine's Luhansk region, which Russia blamed on Ukraine.

"We've seen the Russians claim that this was a Ukrainian attack on this. We do not believe that is true," the official said. "We do believe that the Russians are responsible, but exactly what they used when they did it, why they did it, what the damage is, we just don't have that level of detail," the official said.

The official also noted that a small number of Ukrainians currently in the U.S. for "professional military education" were pulled aside for a couple days of training on Switchblade drones, which the U.S. is sending overseas as part of its military aid, according to the official.

"Although it's not a very difficult system to operate, we took advantage of having them in the country to give them some rudimentary training on that," the official said.

-ABC News' Matt Seyler