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

U.S. President Joe Biden arrived in Brussels on Thursday morning ahead of an emergency NATO summit to discuss the Western defense alliance's response to Russia's invasion of Ukraine.

The European diplomatic capital is also hosting a gathering of the Group of Seven industrialized nations and a summit of the 27 members of the European Union on Thursday. Biden is scheduled to attend all three meetings and hold a press conference at the end of the day.

Upon his arrival at NATO headquarters, Biden was greeted by NATO Secretary-General Jens Stoltenberg. The two leaders stood and spoke for a few moments, though their conversation was inaudible. Biden and Stoltenberg then walked into the building and down the hallway, where they did not stop to speak to reporters who asked whether Russia's potential use of chemical weapons in Ukraine are a red line that would trigger a response from NATO.

Biden and Stolenberg will now meet privately before taking a photo with other NATO leaders.

Earlier Thursday, U.K. Prime Minister Boris Johnson faced the same question from reporters when he arrived at NATO headquarters.

"Look, I think that the reality is that President Putin has already crossed a red line in barbarism and it's now up to NATO to consider together the appalling crisis in Ukraine, the appalling suffering of the people of Ukraine," Johnson replied. "And see what more we can do to help the people of Ukraine protect themselves. See what more we can do to tighten the economic vice around the Putin regime."

-ABC News' Justin Gomez, Molly Nagle and Cecilia Vega

Ukrainian Defense Minister Oleksiy Reznikov on Thursday lambasted Russia's military as "a gang of terrorists, criminals and cowards" who she claimed are committing war crimes.

In a statement posted on her official Facebook account, Reznikov marked one month since Russian forces invaded Ukraine and warned that Ukrainians "still have a very difficult period ahead."

"The Russian military machine will not stop until it is drenched in the blood of its soldiers," Reznikov said.

Earlier this month, Russian troops opened fire on a nursing home in the eastern Ukrainian city of Kreminna, killing 56 people, according to Reznikov.

"This is not an accidental hit," she said. "This is the deliberate killing of defenseless people -- a war crime. That's why the Russian army is a gang of terrorists, criminals and cowards."

Still, Reznikov remained confident that Ukrainian forces will prevail with international support.

"We will drive them out. We will rebuild everything," she added. "We will clean our land from the effects of war. It will take a lot of effort and time."

-ABC News' Julia Drozd

Top Russian defense and military leaders have repeatedly declined telephone calls from their U.S. counterparts since Russia invaded Ukraine on Feb. 24, according to Pentagon spokesman John Kirby.

Kirby said in a statement Wednesday that, over the last month, U.S. Secretary of Defense Lloyd Austin and Gen. Mark Milley, chairman of the U.S. Joint Chiefs of Staff, "have sought, and continued to seek, calls with" Russian Defense Minister Sergei Shoigu and Gen. Valery Gerasimov, chief of the General Staff of the Russian Armed Forces. But the Russians "have so far declined to engage," he said.

"We continue to believe that engagement between U.S. and Russian defense leaders is critically important at this time," Kirby added.

-ABC News' Matt Seyler

The United States is slamming Russia's plans to reopen its stock market for limited trading on Thursday for the first time in a month since Russian forces invaded Ukraine.

"What we’re seeing is a charade: a Potemkin market opening," White House deputy national security adviser Daleep Singh said in a statement early Thursday. "After keeping its markets closed for nearly a month, Russia announced it will only allow 15% of listed shares to trade, foreigners are prohibited from selling their shares, and short selling in general has been banned. Meanwhile, Russia has made clear they are going to pour government resources into artificially propping up the shares of companies that are trading."

"This is not a real market and not a sustainable model—which only underscores Russia’s isolation from the global financial system," he added. "The United States and our allies and partners will continue taking action to further isolate Russia from the international economic order as long it continues its brutal war against Ukraine."

Shares plunged and the Moscow Exchange was shut down following Russia's invasion of Ukraine on Feb. 24. The heavy restrictions on trading as the exchange opens Thursday morning aim to prevent the kind of massive selloff that took place last moth in anticipation of crushing financial and economic sanctions from Western nations, according to The Associated Press.

-ABC News' Molly Nagle