Linda Thomas-Greenfield, the U.S. ambassador to the United Nations, on Wednesday called for other members of the body to join together and isolate Russia for its “unprovoked, further aggression” against Ukraine.

“Other U.N. member states must recognize the threat before us all today before it is too late. There is no middle ground. Calling for both sides to de-escalate only gives Russia a pass. Russia is the aggressor here,” Thomas-Greenfield said during remarks delivered to the U.N. General Assembly.

She said Russia’s actions will likely cause a refugee crisis and food shortages, stating, “The tidal waves of suffering this war will cause are unthinkable.”

Thomas-Greenfield urged member states to “show Russia that it is isolated and alone in its aggressive actions” as Russia considers its next steps.

“What we can do together is make clear that Russia will pay an even steeper price if it continues its aggression,” Thomas-Greenfield said. 

"This, right here, right now, is a moment when we can save this generation, and the next, from that terrible fate,” she continued. “Now is the time to get off the sidelines.”

A former senior Treasury Department official told NBC News that while it was encouraging that the U.S. and European governments were presenting a united front toward Russia on sanctions, Moscow may interpret these first moves as a sign the West was hesitant to pursue tougher measures.

"This is a reasonable first tranche from the Biden administration, moving in step with what the E.U. is reportedly considering, assuming that there are more incremental aggressions anticipated by Moscow that will need escalation room by the U.S. and its partners," said Brian O’Toole, who is now a fellow at the Atlantic Council.

The measures so far fall short of the promised major banking sanctions promised on both sides of the Atlantic as no significant commercial banks were included, he said.

"They will have impact, undoubtedly, but I fear that Putin may assess the West does not have the stomach to impose truly significant measures given the incremental nature of today's announcement," O’Toole added. "I hope that time proves him wrong, as it is clear he has no intention of stopping with just taking the breakaway territories."

Twitter has suspended or locked the accounts of at least 15 users who were tracking Russian military movements on the platform.

The accounts are part of a relatively new form of journalism that uses the internet to gather images and video (also known as open-source intelligence, or OSINT) in an effort to track and report on violent conflicts. Many of these accounts have been tracking Russian military movements — information that the Russian military might have found problematic if they launched an attack.

Many tech companies use automated systems to moderate their platforms, which can be tricked into banning legitimate accounts through a coordinated flood of false claims. 

A spokesperson for Twitter said the company has reinstated some accounts that were mistakenly suspended.

"We’ve been proactively monitoring for emerging narratives that are violative of our policies, and, in this instance, we took enforcement action on a number of accounts in error," the spokesperson said in an email. "We’re expeditiously reviewing these actions and have already proactively reinstated access to a number of affected accounts."

The spokesperson added that the suspensions were not the result of a "coordinated bot campaign" or "mass reporting."

A first round of European Union sanctions went into effect Wednesday targeting Russian politicians and blocking trade between two breakaway regions in eastern Ukraine that were recognized as independent by Moscow this week.  

All 351 legislators in Russia's Duma, or parliament, who voted in favor of formally recognizing pro-Russian separatist regions in Ukraine had any assets they had in the E.U. frozen, the 27-nation bloc said in a news release. They were also prevented from traveling to E.U. countries.  

Banks involved in financing separatist activities in eastern Ukraine as well as 27 other individuals were also targeted with restrictive measures. 

The self-proclaimed "Donetsk People’s Republic" and "Luhansk People’s Republic" will also be removed from a free-trade deal between the E.U. and Ukraine.

Pyotr Tolstoy, the deputy chairman of the Duma, told the Belgian broadcaster RTBF the sanctions were "worthless" and Moscow is planning a response. He did not give details. 

Charles Michel, president of the European Council, called for an emergency summit of European Union leaders to take place Thursday, according to a letter obtained by CNBC. 

The letter was sent to 27 member-state leaders, who will meet in Brussels. 

“The use of force and coercion to change borders has no place in the 21st century,” Michel wrote.

He continued that Russia’s actions “violate international law and the territorial integrity and sovereignty of Ukraine” as well as “undermine the European security order.”

Michel added that at the meeting, he plans to discuss latest developments, protecting the “rules-based” international order, how to “deal with Russia,” and how to support Ukraine.

The presidents of Ukraine, Lithuania and Poland called on Russia Wednesday to "de-escalate" and "withdraw its armed forces deployed around Ukraine’s borders and in temporarily occupied territories of Ukraine." 

In a statement issued after a meeting in Kyiv, Presidents Volodymyr Zelenskyy of Ukraine, Gitanas Nauseda of Lithuania, and Andrzej Duda of Poland expressed their "strongest condemnation" of Russia's decision to recognize two separatist regions in eastern Ukraine as independent. 

"This unprovoked aggressive step by Russia constitutes yet another blatant violation of the fundamental norms and principles of the international law, including the U.N. Charter, as well as security assurances given to Ukraine in the framework of the 1994 Budapest Memorandum," they said. "Russia deliberately and unilaterally has withdrawn from the Minsk agreements and therefore bears full responsibility for further deterioration of the security situation on the ground."

In addition to calling upon the international community to take "resolute and far-reaching steps" in response to Russia's actions, the world leaders urged Russia to de-escalate the situation and "refrain from taking any further military actions."

"The Presidents of Lithuania and Poland stand by Ukraine and fully commend and support its efforts to solve Russian-Ukrainian conflict by diplomatic and peaceful means," they added.

At least five Ukrainian websites were slowed or rendered inaccessible by a cyberattack on Wednesday, the country's minister of digital transformation, Mykhailo Fedorov, said on his Telegram channel.

The websites of the Cabinet of Ministers and Ministry of Foreign Affairs as well as those of a number of banks were hit with a distributed denial of service (DDoS) attack, Fedorov said. DDoS attacks are a simple tactic to overwhelm a website with massive amounts of traffic.

The attack echoes a similar one last week, which Ukraine and the U.S. attributed to Russia. That case appeared to have been a hybrid information warfare tactic designed to harass Ukrainians and sow distrust about their financial systems. Hackers knocked out the websites of two major banks while simultaneously sending many Ukrainians spam text messages that informed them ATMs were down.

Ukrainian frontier guards patrol an area along the Ukrainian-Russian border in the Kharkiv region on Wednesday.

Russia has remained defiant in the face of fresh sanctions from the United States and other Western nations, saying the penalties will "not affect our resolve to keep standing up for our interests" as it warned of a "strong response."

In a statement Wednesday, Russia's foreign ministry said the new sanctions were "in line with Washington's unceasing attempts to change Russia's course." 

"Despite the obviously barren efforts that have been taken over many years to halt the development of our economy, the USA are grabbing the restricting instruments again, which are ineffective and counterproductive for the America’s own interests," the ministry said, adding that "Russia has proved that it can minimize the losses of these sanctions."

The foreign affairs ministry said the U.S. was following a "false conviction" that it "still has the right to impose its own rules of the world order."

The ministry said Russia was open "only toward diplomacy that is based on principles of mutual respect, equality and consideration of each other’s interests."

It also said there would be a "strong response" to the sanctions. "Not necessarily a symmetrical one, but measured and considerable for the American side."