Russia-Ukraine updates: US sanctions Russian military shipbuilder, diamond miner

President Joe Biden on Wednesday spoke in-depth for the first time about the horrific images of civilian deaths in the Ukrainian city of Bucha.

"I'm sure you've seen the pictures from Bucha and just outside of Kyiv, bodies left in streets as Russian troops withdrew. Some shot ... with their hands tied behind their backs. Civilians executed in cold blood," Biden said at the North America's Building Trade Union legislative conference in Washington, D.C.

"Bodies dumped into mass graves… There is nothing less happening than major war crimes," he said.

Biden called on responsible nations to “come together to hold these perpetrators accountable."

"The steps we're already taken are predicted to shrink Russia's gross domestic product by double-digits this year alone. Just in one year, our sanctions are likely to wipe out the last 15 years of Russia's economic gains and because we've cut Russia off from important technologies like semiconductors and encryption security and critical components of quantum technology that they need to compete in the 21st century. We're going to stifle Russia’s ability in its economy to grow for years to come," Biden said.

-ABC News' Molly Nagle

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

Treasury Secretary Janet Yellen testified before the House Committee on Financial Services that the Treasury would continue to take steps to prevent Russia from participating in the international financial system.

"Russia's actions, including the atrocities committed against innocent Ukrainians in Bucha, are reprehensible, represent an unacceptable affront the rules based global order and will have enormous economic repercussions in Ukraine and beyond," she said.

Yellen said the International Monetary Fund and World Bank have assisted Ukraine, allowing the country "fiscal space to pay salaries for civilians, soldiers, doctors and nurses."

Rep. Patrick McHenry, R-N.C., asked Yellen why the U.S. continues to provide licenses that permit certain bank transactions related to Russian energy despite a ban on Russian oil imports. Yellen said that although the sanctions aim to cripple Russia’s economy, some of the U.S.'s European allies are still dependent on Russian gas.

"Our goal from the outset has been to impose maximum pain on Russia while, to the best of our ability, shielding the United States and our partners of undue economic harm," she said. "Unfortunately, many of our European partners remain heavily dependent on Russian natural gas as well as oil."

-ABC News' Armando Tonatiuh Torres-García

Hugh Williamson, director of the Human Rights Watch's Europe and Central Asia division, wrote in an OpEd in the Telegraph that the HRW is racing to document war crimes in Ukraine.

Williamson said one apparent war crime was when seven Ukrainian civilians were allegedly executed by Russian soldiers.

Regarding the images of civilian bodies in the Ukrainian town of Bucha, Williamson said they're concerned many of the deaths may be the result of war crimes, but "it's too early to say for certain now, and legal proceedings are still at a nascent stage."

This comes as a spokesperson for Russia's Ministry of Foreign Affairs doubled down on Russian claims that civilian killings in Bucha were staged.

"On April 3, the world witnessed another crime by the Ukrainian authorities, this time in the town of Bucha, where a criminal false flag operation [showing] the alleged killing of civilians by Russian troops had been staged," Russian Foreign Ministry spokesperson Maria Zakharova said at a briefing on Wednesday according to state-run TASS. Zakharova claimed that when Bucha was controlled by the Russian Armed Forces, not a single local resident was affected by acts of violence.

-ABC News' Christine Theodorou