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

Russian President Vladimir Putin's partial military mobilization for his ongoing war in neighboring Ukraine is "definitely a sign that he's struggling," according to the White House's National Security Council spokesman John Kirby.

"And we know that," Kirby told ABC News' George Stephanopoulos during an interview Wednesday on "Good Morning America."

"[Putin] has suffered tens of thousands of casualties. He has terrible morale, unit cohesion on the battlefield, command and control has still not been solved. He's got desertion problems and he's forcing the wounded back into the fight," Kirby added. "So clearly manpower's a problem for him, he feels like he's on his back foot, particularly in that northeast area of the Donbas."

Some 300,000 Russian reservists are expected to be conscripted, which Kirby noted is "a lot."

"That's almost twice as much as [Putin] committed to the war back in February," he said.

Kirby said Putin's latest nuclear threats are "typical" but something the United States and its allies still take "seriously."

"We always have to take this kind of rhetoric seriously," he added. "It's irresponsible rhetoric for a nuclear power to talk that way, but it's not atypical for how he's been talking the last seven months and we take it seriously. We are monitoring as best we can their strategic posture so that if we have to, we can alter ours. We've seen no indication that that's required right now."

And if Russia does use nuclear weapons, "there will be severe consequences," according to Kirby.

While Moscow appears poised to annex Russian-held regions in Ukraine and attempt to politically legitimize it with sham referendums in the coming days and weeks, Kirby said the United States will still consider those areas Ukrainian territory.

"We're going to continue to support Ukraine with security systems and other financial aid, as the president said, for as long as it takes," he added. "That is Ukrainian territory. It doesn't matter what sham referendum they put in place or what vote they hold, it is still Ukrainian territory."

3:18

John Kirby talks Putin's move to call up more troopsThe national security council coordinator for strategic communications at the White House discusses Russia's latest war strategy in Ukraine.

ABCNews.com

Russian President Vladimir Putin has ordered a partial mobilization of reservists in Russia, in an apparent admission that his war in neighboring Ukraine isn't going according to plan.

In a seven-minute televised address to the nation that aired on Wednesday morning, Putin announced the start of the mobilization -- the first in Russia since World War II. The measure is expected to draft more than 300,000 Russian citizens with military experience, according to Russian Defense Minister Sergei Shoigu.

The move comes as Moscow is poised to annex all the regions it occupies in Ukraine in the coming weeks, with plans to hold sham referendums this weekend in an effort to politically legitimize its actions. By declaring those areas officially Russian territory, Putin is also threatening that any continued efforts by Ukraine to retake them will be seen as a direct attack on Russia. In his speech Wednesday, the Russian leader raised the specter of using nuclear weapons if Ukraine continues to try to liberate the occupied regions.

"In the event of a threat to the territorial integrity to our country, for the protection of Russia and our people, we of course will use all means in our possession," Putin said. "This is not a bluff."

"Those who are trying to blackmail us with nuclear weapons should know that the wind can turn in their direction," he added.

It's an attempt to regain the initiative after disastrous setbacks in Russia's war against Ukraine.

Russia has been suffering severe manpower shortages in Ukraine after months of heavy losses, mainly because the Kremlin has pretended it is fighting not a war but a "special military operation." That, in part, allowed Ukraine's spectacular counteroffensive in the country's northeast two weeks ago, which led to the collapse of Russia's frontline there.

Military experts and Russian commentators themselves had acknowledged that without a mobilization, Moscow is not capable of anymore offensive operations in Ukraine and in the longterm might well be unable to even hold the territory it has already taken.

Putin has balked at ordering a mobilization, until now, because of the huge political risks it carries for him at home. Russians have proved relatively supportive of the war while they have not been ordered to fight it, but this carries much bigger risks now of domestic unrest. It will bring up dangerous memories of the Soviet disaster in Afghanistan and Chechnya.

Yet Putin has clearly decided he must take the risk, with losing the war in Ukraine seen as an existential danger to his regime.

The mobilization order has profound implications for not just Russia and Ukraine, but also for Europe and the United States. It means Putin is expanding the war in Ukraine even further, ready to throw hundreds of thousands more people into it -- making the fight harder again for Ukraine, while also raising the threat of nuclear strikes on it. And at home, Putin is going to enter uncharted waters.

-ABC News' Patrick Reevell and Tom Soufi Burridge

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Putin declares partial mobilization as war in Ukraine escalatesLegislation being pushed through Russia's parliament lays the groundwork for a general mobilization, forcing men over the age of 18 to fight in Ukraine.

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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