WASHINGTON — The United States, working in coordination with Europe, imposed new sanctions on prominent Russian officials on Monday as the showdown over Ukraine reached a new stage of confrontation between East and West.

President Obama signed an executive order freezing the assets and banning visas for a number of Russians deemed to be responsible for the seizing of Crimea or otherwise interfering in Ukrainian sovereignty. Among those targeted were several officials in President Vladimir V. Putin’s inner circle, and the White House threatened to go after more if Russia did not back down.

“We have fashioned these sanctions to impose costs on named individuals who wield influence in the Russian government and those responsible for the deteriorating situation in Ukraine,” the White House said in a statement. “We stand ready to use these authorities in a direct and targeted fashion as events warrant.”
In a conference call briefing reporters, a senior administration official who was not permitted to be named under the ground rules said, “These are by far the most comprehensive sanctions applied to Russia since the end of the Cold War — far and away so.”

Among those targeted were Vladislav Surkov, one of Mr. Putin’s most influential advisers, known as the Kremlin’s “gray cardinal”; Sergei Glazyev, an economist who has been advising Mr. Putin on Ukraine; Valentina Matviyenko, chairman of the Federation Council, the upper house of Parliament; and Dmitry Rogozin, a deputy prime minister. No sanctions were placed on Mr. Putin.

Others named by the White House were Leonid Slutsky and Yelena Mizulina, members of the State Duma, the lower house of Parliament; and Andrey Klishas, a member of the Federation Council who wrote a bill to seize assets of Western individuals and assets in retaliation for any sanctions imposed on Russia.

The White House also sanctioned two Russian-supported figures who have taken power in Crimea — Sergei Aksyonov, the newly declared prime minister; and Vladimir Konstantinov, the newly declared speaker of its Parliament. It also targeted Viktor F. Yanukovych, the pro-Russian Ukrainian president deposed in February; and Viktor Medvedchuk, head of a pro-Russian civil society group, Ukrainian Choice.

The sanctions came the day after a Moscow-supported referendum in Crimea in which local authorities claimed a 97 percent vote in favor of breaking off from Ukraine and rejoining Russia. The new Crimean government on Monday declared itself independent as it seeks annexation from Russia.

Mr. Obama told Mr. Putin in a telephone call on Sunday that the referendum “violates the Ukrainian Constitution and occurred under duress of Russian military intervention” and “would never be recognized by the United States and the international community.” He continued to stress, however, that “there remains a clear path for resolving this crisis diplomatically.”

European officials approved their own sanctions on Monday, targeting 21 individuals. Their list overlapped to some extent with the American list, according to Obama administration officials; however, the names will not be released until Tuesday.

In taking his action on Monday, Mr. Obama signed a new executive order intended to broaden the sanctions authority he already approved. Aides said he was targeting three broad categories of people: Russian government officials, arms sector figures, and others deemed to be working on behalf of Russian senior officials, the latter called “Russian government cronies” by a senior American official.

The order means that any assets owned by the targeted Russians in the United States will be frozen and Americans will not be allowed to do business with them. If they want to transact in dollars, they will no longer be able to do so, officials said. And the American action will influence foreign banks and other institutions not to do business with these Russians, officials said.

The sanctions are the second round approved by Mr. Obama. The first round banned visas for nearly a dozen Russian and Ukrainian individuals but did not include financial measures.

Mr. Obama held off a more expansive target list on Monday to leave room for future action if necessary. “We have the ability to escalate our actions in response to Russian actions,” a senior administration official told reporters on a conference call under ground rules that did not permit him to be identified. (Source: The New York Times)