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

U.S. Attorney General Merrick Garland met Tuesday with Ukrainian Prosecutor General Andriy Kostin and signed a memorandum of understanding to strengthen their investigative partnership in pursuing prosecutions against Russians accused of committing war crimes in Ukraine.

"America and the world have seen the horrific images and the heart-wrenching reports of the brutality and death caused by the unjust Russian invasion of Ukraine," Garland said following the meeting at the Department of Justice in Washington.

Garland said the DOJ's War Crimes Accountability Team has provided Ukraine with a "wide variety" of technical assistance on criminal cases, including collecting evidence and forensic analysis.

The memorandum of understanding, Garland said, will allow the two countries to "work more expeditiously and efficiently" in their investigations of Russian war crimes.

Kostin also delivered somber remarks on war crimes uncovered by Ukrainian investigators since the start of the Russia's invasion. He said that two hours before his meeting with Garland, a prosecutor in the Kharkiv region of Ukraine informed him of a village "where about 100 graves" were just discovered.

"This place is not safe at the moment since it needs de-mining," Kostin said. "But this is a new example of mass atrocities by the aggressor. This is a sign that Russia uses not only prohibited means and methods of warfare, but this is a clear and intentional policy of Russia."

-ABC News' Alexander Mallin

The impact on crop production due to Russia's invasion of Ukraine will likely continue to increase global food prices and food insecurity, though not as much as initially feared, according to a new study.

The price of corn and wheat are expected to increase by 4.6% and 7.2%, respectively, and crops such as barley, rice, soybeans and sunflower are also anticipated to rise, according to a study from Indiana University published this week in Nature Food.

Nations with current existing food insecurity will be most impacted by the conflict, according to the study.

Other countries, including Brazil, have stepped up their production to fill the gap left by the lack of exports coming out of the region, offsetting some of the impacts on world food prices and food insecurity, the study found. Clearing more land and vegetation to grow crops could increase deforestation and carbon emissions, the study said.

-ABC News' Tracy Wholf

U.S. national security adviser Jake Sullivan said referendums planned for this week in Russia-backed areas of eastern and southern Ukraine are a "sham."

"Russia is throwing together sham referendums on three days notice as they continue to lose ground on the battlefield and as more world leaders have distanced themselves from Russia on the public stage," Sullivan said in a briefing Tuesday at the White House.

He also slammed legislation being pushed through the Russian parliament to lay the ground for a general mobilization of men aged 17-27 as "scraping for personnel to throw into the fight."

“These are not the actions of a confident country. These are not acts of strength, quite the opposite," Sullivan said. "We reject Russia's actions unequivocally."

-ABC News' Ben Gittleson

The Kremlin made a series of dramatic announcements Tuesday, signaling its response to its failing military campaign in Ukraine.

The Kremlin said referendums will be held later this week in Russian-backed regions of eastern and southern Ukraine for people to vote on whether to join Russia.

Dmytro Kuleba, the Ukrainian minister of foreign affairs, called the proposed vote "sham referendums" in a post on Twitter.

"Russia has been and remains an aggressor illegally occupying parts of Ukrainian land," Kuleba said. "Ukraine has every right to liberate its territories and will keep liberating them whatever Russia has to say."

Depending on the results of the referendums, which critics say is a foregone conclusion, Russia will suddenly consider territory it has occupied in Ukraine as its own.

Meanwhile, legislation is being rushed through the Russian parliament, laying the ground for a general mobilization of men aged 17-27, an age range that could be expanded.

Russian state media reported that Russian President Vladimir Putin and his minister of defense will address the nation Tuesday night.

According to a Moscow-based military analyst, even parts of Ukraine's eastern Donbas, which are not currently controlled by Russian forces, will be considered Russian territory.

After its apparently successful offensive in northeastern Ukraine, the Ukranian military now appears to be pushing further east and is contesting areas of the eastern Donbas region.

In a highly symbolic moment, Ukrainian forces claim they have retaken a village in Luhansk, in the northern part of the Donbas, an area the Kremlin took control of in July.