The U.S. and Europe will bar some Russian banks from SWIFT.

The Biden administration and key allies announced on Saturday that they would remove several of the largest Russian banks from the financial messaging system. They said they would impose new restrictions on Russia's central bank to prevent it from using its large international reserves to undermine sanctions.

The actions agreed to by the European Commission, Britain, Canada, France, Germany, Italy and the United States were significant in their effort to impose severe economic costs on Russia.

The countries said in a joint statement that they are committed to defending the international rules that have prevailed since the Second World War.

The action was a remarkable change of direction for European powers that, until recently, were reluctant to end a 30-year effort to integrate Russia in the European economy. European nations seem to be moving toward a policy of containment.

They stopped short of barring energy transactions with Russia. The result is that Germany, Italy and other European nations will continue purchasing and paying for natural gas that flows through the Russian and Ukrainian pipes.

In an effort to bring the Russian economy to its knees, President Volodymyr Zelensky of Ukraine and some in Europe called for all Russian institutions and individuals to be cut off from SWIFT. 40 percent of the Russian government's budget comes from energy sales.

Ursula von der Leyen, the president of the European Commission, said that cutting banks off will stop them from conducting most of their financial transactions worldwide.

Ms. von der Leyen said that the trans-Atlantic coalition would try to cripple Russia's central bank by freezing its transactions and making it impossible for it to liquidate assets.

The targeting of Russia's central bank could prove more consequential than the SWIFT measures. Russia has spent the last several years bolstering its defenses against sanctions, amassing more than $630 billion in foreign currency reserves. The ruble's value has fallen dramatically amid the latest rounds of sanctions.

The country's ability to support its currency in the face of new sanctions is under threat, as Biden administration officials said on Saturday. That could cause inflation, and the administration is hoping that will lead to protests against Mr. Putin in Russia.

The Center for a New American Security believes that Russia has been taking steps since the beginning of the year to protect its economy from sanctions.

The United States and its allies put pressure on Russia's elites. A senior American official told reporters on Saturday that Europe and the United States would create a task force to identify, hunt down and freeze the assets of Russian companies that are subject to sanctions.

The goal is to undermine the ability of people who are close to Mr. Putin to live in both Russia and the West. The United States and its allies said that they will limit the sale of golden passports that allow wealthy Russians who are connected to the Russian government to become citizens of Western nations and gain access to their financial systems.

The announcement falls short of a blanket cutoff of Russia from SWIFT, which some officials see as a nuclear option of sorts. It would have severed Russia from the global financial system.

Some experts say that it may only drive Russia to expand the alternative to the SWIFT system that it created several years ago when it began attempting to besanction-proof. Russia's equivalent system is mostly domestic, so it would have to team up with China.

On the same day that Germany's chancellor announced that his government was approving a transfer of antitank weapons to the Ukrainian military, the moves on Saturday came.

Germany's foreign minister and its economy minister acknowledged in a post that the country's government was moving from opposing a ban to favoring a narrowly targeted one.

They wrote that they are working on how to limit the damage of a disconnection from SWIFT so that it hits the right people.

European officials have said that they had tense discussions with American and British officials who were pressing for a cutoff of the international money transfer service.

Some American officials had reservations about severing Russia completely. It could erode the ability of the United States to track and control payments if it speeds the development of alternatives to the SWIFT system that Russia and China have been developing.

The announcement did not say which banks would be cut off.

The Society for Worldwide Interbank Financial Telecommunication is a Belgian service that connects more than 11,000 financial institutions around the world. It doesn't hold or transfer funds, but lets banks and financial institutions alert each other of transactions about to take place.

While all options were on the table, the Biden administration played down the idea of cutting Russia off from the system, suggesting that such a move could create more problems than it would solve.

Behind the scenes, American officials were pressing European allies to give some kind of indication to Mr. Putin that Europe was moving toward greater economic isolation of Russia.

European countries have been allowed by the United States to take the lead on the issue. If the United States continued to transmit messages for Russian institutions, it would be able to impose sanctions on the organization itself.

Some experts on sanctions argue that banning Russian financial institutions from the international money transfer network is not a good way to punish Russia. Some argue that blocking Russian institutions from the system would hurt the country's financial sector and that choosing only a few banks to remove from the system does not go far enough.

The assistant Treasury secretary for terrorist financing in the Trump administration said that a targeted cutoff would not achieve what is needed. The more straightforward approach is to detach from all of the Russian financial institutions.

Alan Rappeport and David E. Sanger reported from Washington.

The world woke up on Thursday to the possibility of an all-out war in Europe after President Putin of Russia ordered his troops to invade Ukraine. Millions of people in Ukraine and Eastern Europe were wondering how the conflict would affect their lives.

Estimates of tens of thousands of deaths over the course of the conflict are based on reports of 40 Ukrainian solders killed in the hours after the invasion. Economic penalties to punish Russia will be felt worldwide.

Consumers will be hurt by rising energy costs and slowing supply chains. Russian cyberattacks could cripple electronic infrastructure. There will be a new refugee crisis. Since the end of the Cold War, there has been relative calm in the West.

What might happen next on the military, economic and diplomatic fronts.

NATO said on Thursday that it was sending reinforcements to its eastern flank, joining the 6,500 U.S. troops already dispatched to Eastern Europe and the Baltics.

NATO said in a statement that they are increasing the readiness of their forces to respond to all.

About 1,000 troops are being redeployed in Europe. Some 800 U.S. troops are moving from Italy to the Baltics, while 20 Apaches are going from Germany to Poland. The Pentagon said that eight F-35 strike fighters are heading from Germany.

A spokesman for the US Army said on Thursday that troops from the 101st Airborne and the 82nd Airborne are preparing to move closer to Poland's border with Ukraine to help process people fleeing the country.

Many of the troops from the 18th Airborne Corps who arrived in Poland this month have been working with the State Department and Polish forces to set up three processing centers near the border to help deal with tens of thousands of people, including Americans, who are expected to flee Ukraine.

In Jasionka, Poland, an indoor arena has bunk beds and supplies for up to 500 people. In Austria, Chancellor Karl Nehammer said he was willing to accept refugees. Relief organizations that provide food, water, shelter and emergency health care to people who have fled the violence in the region are funded by the State Department and the U.S. Agency for International Development.

In the days to come, the C.I.A. will assess what kind of assistance it can provide. If a Ukrainian resistance develops in parts of the country that Russia seeks to control, the agency could secretly supply partisan forces with intelligence and weaponry.

Mick Mulroy is a former C.I.A. paramilitary officer and senior Pentagon official.

The administration has studied how sanctions would affect each of the big banks. Sberbank has a third of the assets in the country's banking sector. Some experts are skeptical that the administration would put those two banks on the S.D.N. list for fear of the consequences for the Russian and global economies. Swift is the important Belgian money transfer system used by more than 11,000 financial institutions worldwide.

There are other sanctions lists that impose costs while not causing a lot of suffering. It could place a bank on a list that prevents it from doing transactions involving dollars. U.S. dollars are the currency that underpins the global economy.

Russian officials, business people and companies are expected to be put on the sanctions list by the Treasury Department.

The nation's stock market had fallen nearly 40 percent by Thursday afternoon.

The Commerce Department is trying to restrict the export of certain American technologies to Russia, a tactic that the Trump administration used against the Chinese telecommunications company. The supply chain would be damaged by the controls. The defense industry and the oil and gas industry were targets, according to U.S. officials.

European officials are expected to announce similar sanctions as they did this week. They have been more cautious about imposing the toughest sanctions because of the strong trade with Russia.

Although Mr. Biden has said he will contemplate any possible sanctions, U.S. officials are not planning on disrupting Russia's energy exports. Europe depends on the products and rising oil prices would cause inflation and problems for politicians. This week, Germany announced that it would not certify the new natural gas line, which would connect Russia and Western Europe. The sanctions were announced by Mr. Biden on a subsidiary of the Russian energy company.

The measures we have and are prepared to impose on the Russian Federation won't be free for the Russian.

Mr. Biden is grappling with voter frustration over inflation less than nine months before the elections.

Republicans are expected to criticize Mr. Biden and Democrats because of the domestic economic hardship. A group of Republicans led by President Donald J. Trump has praised Russia and criticized Mr. Biden for his policies. Analysts say that Mr. Putin sees political division as a strategic advantage.

The State Department moved its personnel from Ukraine to Poland as it continued to offer assistance to American citizens who want to leave the country. Mr. Price estimated that there were far fewer Americans in Ukraine than there were in the fall.

The larger question for the rest of the world is whether Mr. Putin's invasion has irrevocably broken international systems in which Russia has been seen as a legitimate contributor.

The events of last night are a turning point in the history of Europe and of our country, according to the President of France.

The diplomats from NATO, the U.N. Security Council and the European Council were going to meet later on Thursday to plot out the next steps. At the Security Council, the United States urged others to join a resolution condemning Russia's aggressions. Humanitarian aid to Ukrainian refugees and access for relief workers are included in the effort that will be put to a vote on Friday.

Russia has a permanent veto on the council, meaning it could derail a resolution to rein in Mr. Putin.

Secretary of State Antony J. Blinken may travel to Europe next week to meet allies and ensure that a unified front against Russia remains. He canceled the meeting with the Russian foreign minister because he said it was pointless as Russian troops took up battle formations.

On Wednesday night, even as he predicted that an assault was imminent, Mr. Blinken issued an 11th-hour appeal for Mr. Putin to take a diplomatic path from conflict.

If Russia demonstrates that it is serious about it, we will pursue that. We are prepared to try to avoid this through dialogue. If Russia decides to choose a path of aggression, we are prepared.

It was not clear if that path had been closed.

The reporting was contributed to by two people.