THE HAGUE — The United States and its closest allies on Monday cast Russia out of the Group of 8 industrialized democracies, their most exclusive club, to punish President Vladimir V. Putin for his lightning annexation of Crimea, while threatening tougher sanctions if he escalates aggression against Ukraine.
President Obama and the leaders of Canada, Japan and Europe’s four strongest economies gathered for the first time since the Ukraine crisis erupted last month, using a closed two-hour meeting on the sidelines of a summit meeting about nuclear security to project a united front against Moscow.
But they stopped short, at least for now, of imposing sanctions against what a senior Obama administration official called vital sectors of the Russian economy: energy, banking and finance, engineering and the arms industry. Only further aggression by Mr. Putin — like rolling his forces into the Ukrainian mainland — would prompt that much-harsher punishment, the countries indicated in their joint statement, called the Hague Declaration.
“The biggest hammer that can drop is sectoral sanctions, and the clearest trigger for those is eastern and southern Ukraine,” the senior administration official said.
Some critics of the administration said the suspension of Russia from the G-8, which administration officials acknowledged was largely symbolic, showed a lack of resolve among the allies to take tougher steps to undo Mr. Putin’s annexation of Ukraine.
But it signified a firming of Western resolve compared with the early days of the Crimea crisis, when Germany and some other allies said it was premature to consider excluding Russia from the club of industrial democracies. Having Russia as part of that group since 1998 was meant to signal cooperation between East and West, and its exclusion inevitably raises new echoes of Cold War-style rivalry.
Announcing that they would boycott a Group of 8 meeting planned for Sochi — Mr. Putin’s Black Sea showcase for the recent Winter Olympics — the seven countries who met here said they would instead gather by themselves in June in Brussels, headquarters of NATO and the European Union.
“We will suspend our participation in the G-8 until Russia changes course,” the seven countries declared in what constituted a subtle appeal to Russian leaders outside Mr. Putin’s circle to press for a switch in direction.
After the Soviet Union collapsed in 1991, Russia eagerly sought to join the tight circle of the world’s top economies, eventually gaining entry in 1998. For all that Mr. Putin shrugged off the threat of canceling the Sochi summit this month — a shoulder shrug imitated here by his foreign minister, Sergey V. Lavrov, on Monday — it is a blow to the Kremlin’s search for prestige.
Mr. Putin took membership in the group so seriously that he went all out when it came time for Russia to host the annual meeting for the first time. He rebuilt a broken-down czarist-era palace outside his hometown, St. Petersburg, in part with the summit in mind, adding a series of new mansions to the grounds for each leader to stay in. The Kremlin hired a Western public relations agency to promote its status as host.
“Obviously, it’s mostly symbolic, but symbols do matter,” said Michael A. McFaul, the just-departed American ambassador to Moscow. “The G-8 was something they wanted to be part of. This for them was a symbol of being part of the big-boy club, the great power club — and the club of democracies, I might add.”
The Obama administration voiced satisfaction that the West was united in punishing Russia, both now and in future, if it does not reverse course. “There really wasn’t much disagreement” at the meeting either about Russia or the need to swiftly aid Ukraine, the senior administration official said.
Germany’s chancellor, Angela Merkel, who with her foreign minister has had the most contact with Mr. Putin and other Russian officials during this crisis, has been among the most forthright in rejecting Mr. Putin’s actions, despite the potential costs to Germany’s economy.
German businesses sold almost 40 billion euros of goods to Russia last year, and bought Russian imports of the same value, almost exclusively oil and natural gas supplies that meet about one-third of Germany’s energy needs.
But Ms. Merkel has strengthened Germany’s response over the past two weeks after she perceived Mr. Putin as violating promises by annexing Crimea and opting for old-fashioned nationalism and the use of military force over the talk of cooperation and respect for borders that have governed East-West relations in recent decades.
The support of Germany, the largest economy in Europe and a longtime bellwether on Russian relations, is viewed as crucial to enforcing tougher sanctions if they become necessary down the road. The administration official said that any such sanctions would have “consequences for the global economy and individual countries.”
“The cost is far greater for the Russians, who stand much more to lose,” the official added.
Russia argues that Crimea has effectively been Russian territory since the 18th century and was put under Ukrainian sovereignty only by the Soviet leader Nikita S. Khrushchev in 1954 as a gesture of good will inside the Soviet Union. It says its military intervention was meant to protect Russian speakers from Ukrainian nationalists who helped topple the previous, more pro-Russian government.
But Western leaders have condemned the military incursion as a violation of both international law and specific Russian agreements with Ukraine and the outside world, and disputed Russian claims that ethnic Russians faced threats to their safety.
The leaders met on the sidelines of a nuclear security summit arranged in advance of the Ukraine crisis. Ms. Merkel, speaking to German reporters, noted that the two issues were deeply linked. Ukraine, she recalled, renounced its Soviet-era nuclear weapons in 1994 by concluding the Budapest Memorandum, an agreement with the United States, Britain and Russia to guarantee the integrity of Ukraine.
That accord “has been flagrantly violated,” she noted.
Ban Ki-moon, the secretary general of the United Nations, stressed in a speech to the full summit meeting that he worried some current or future nuclear powers could view the weapons as crucial to protect themselves against invasion, undermining hopes of reducing their spread.
“Nuclear weapons should be seen as a liability and not an asset,” he said.
Also on the sidelines of the nuclear summit meeting, Mr. Lavrov held talks with his Ukrainian counterpart, Andriy Deshchytsia, for the first time since Russia’s move into Crimea. The two defense ministers spoke by telephone last week, but the meeting — about which little was revealed — was the first such face-to-face encounter between members of the current governments in Moscow and Kiev.
There was no mention in the Monday declaration of how much assistance the West will now give Ukraine, either in cash or in bolstering a relatively weak acting government until elections scheduled for May 25.
Ukraine has said it needs €1 billion in immediate assistance, and the European Union is readying a further €11 billion, or about $15 billion, for this year, mostly through lending by European institutions. The declaration emphasized instead the “central role” of the International Monetary Fund in “lessening Ukraine’s economic vulnerabilities, and better integrating the country as a market economy in the multilateral system.”
“We remain united in our commitment to provide strong financial backing to Ukraine,” The Hague Declaration said, specifying that it would bolster trade and strengthen security in the key field of energy.
European powers that depend heavily on Russia for natural gas also indicated that they would pursue a strategy to reduce dependence on Russian energy by June, though any effort to shift suppliers is likely to take many months or years.