Ukrainian troops have retaken "key terrain" in the north of the country, "after denying Russia the ability to secure its objectives and forcing Russian forces to retreat" from areas around Chernihiv and north of Kyiv, the U.K. Ministry of Defense said in an intelligence update Tuesday.

"Low-level fighting is likely to continue in some parts of the newly recaptured regions, but diminish significantly over this week as the remainder of Russian forces withdraw," the ministry added. "Many Russian units withdrawing from northern Ukraine are likely to require significant re-equipping and refurbishment before being available to redeploy for operations in eastern Ukraine."

Ukrainian President Volodymyr Zelenskyy indicated Tuesday that peace talks with Russia may now be off the table, following the gruesome discovery of scores of dead civilians in Bucha and other towns outside Ukraine's capital that were recently recaptured from Russian forces.

"The most difficult thing is to talk about what they did," Zelenskyy told reporters in Kyiv. "We believe that this is genocide. We believe that they should be punished for it."

"I believe that we need to set such a bar for these negotiations," he added. "It may happen that there will be no meeting."

Zelenskyy's comments came a day after he traveled to Bucha, northwest of Kyiv, where bodies in civilian clothes were found strewn in the streets and in mass graves. Many of the victims appeared to have been shot at close range and some even showed signs of torture. ABC News journalists on the ground saw some of the dead, including a family that locals said were executed with their hands bound.

-ABC News' Yulia Drozd

Russia's communications and media regulator, Roskomnadzor, is demanding that Wikipedia remove content that contradicts the Kremlin's narrative about the war in Ukraine.

"Based on a motion from the Russian Prosecutor General's Office, Roskomnadzor demanded on April 4 that the Wikipedia management put an end to the dissemination of false socially significant information," the agency said in a statement Tuesday. "Materials containing false information about the special military operation in Ukraine and operations of the Russian Armed Forces have been massively published on Wikipedia in the recent period. Wikipedia has become a new line for continuous information attacks on Russians."

Roskomnadzor accused the free online encyclopedia of "deliberately" misinforming Russian users. The agency noted that it has previously asked Wikipedia "to remove false information about events in Ukraine" and threatened to fine the San Francisco-based company up to 4 million rubles (about $47,000) for failing to delete such content, which is illegal under Russian law.

The U.S. Treasury said Monday night that it would no longer allow the Russian government to make payments on debt using dollars it holds at U.S. financial institutions, another step that puts pressure on the Russian government’s funds.

This step “was in the works before the weekend and isn’t a response” to the atrocities in Bucha, according to a Treasury spokesperson.

"One of the most potent actions of the 700-plus sanctions we’ve imposed have been our sanctions on Russia’s Central Bank, which were levied with unprecedented multilateral coordination, speed, and impact," the spokesperson said. “Today is the deadline for Russia to make another debt payment. Beginning today, the U.S. Treasury will not permit any dollar debt payments to be made from Russian government accounts at U.S. financial institutions.”

"Russia must choose between draining remaining valuable dollar reserves or new revenue coming in, or default," the spokesperson continued. "This will further deplete the resources Putin is using to continue his war against Ukraine and will cause more uncertainty and challenges for their financial system."

-ABC News' Ben Gittleson

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