By Mark Landler, Annie Lowrey and Steven Lee Myers

New York Times News Service

WASHINGTON — President Barack Obama expanded sanctions against Russia on Thursday, blacklisting a bank and several wealthy businessmen with close ties to President Vladimir Putin, as the United States struggled to forestall further Russian incursions into Ukraine.

Among those targeted were Sergei Ivanov, the president’s chief of staff; Gennady Timchenko, a billionaire investor with links to Putin; and Yuri Kovalchuk, whom the administration described as the personal banker for Russian leaders, including the president.

Obama also opened the door to more sweeping measures against core parts of the Russian economy, including the oil and natural gas industries, which account for much of Russia’s exports. He said the actions could disrupt the global economy, but might be necessary because of what he described as menacing movements by the Russian military near eastern and southern Ukraine.

Administration officials insisted that the new sanctions would have more bite than the initial ones Obama announced Monday. But it remains unclear whether they will be enough to put a brake on Putin, who brushed aside the previous measures and moved swiftly to annex Crimea.

Responding almost immediately, Russia barred nine prominent U.S. officials from entering the country, including House Speaker John Boehner; Senate Majority Leader Harry Reid; Sen. John McCain, R-Ariz.; and three close advisers to Obama.

Obama said Russia’s aggressive moves toward Ukraine had only escalated since the referendum in Crimea on Sunday.

“These are all choices that the Russian government has made,” he said, “and because of these choices, the United States is today moving, as we said we would, to impose additional costs on Russia.”

The administration was also prodded by signs that the Russian military had moved troops into positions that could threaten southern and eastern Ukraine. While Obama has ruled out direct military involvement, another senior administration official told reporters that the Pentagon was studying whether to provide communications equipment and other nonlethal assistance to the Ukrainian military.

These sanctions are surgical, experts said: designed to hit the wallets of individuals with close ties to Putin, rather than to damage the broader Russian economy.

“The dollar figure is not big,” said Anders Aslund, a senior fellow at the Peterson Institute for International Economics in Washington. “But these people are really close to Putin.”

The Treasury also designated Bank Rossiya, the 17th-largest Russian bank, of which Kovalchuk is the largest shareholder. A senior official said that would pinch Putin and his friends because Rossiya would no longer be able to conduct transactions in dollars and would find its assets frozen in correspondent accounts in European banks.

Obama said more sweeping sanctions were not his “preferred outcome,” and analysts said they did not expect him to impose them.

“Russia must know that further escalation will only isolate it further from the international community,” he said.

In Russia, officials reacted to the sanctions with a mix of indignation and contempt. Foreign Minister Sergei Lavrov said, “They are illegitimate. They have no international legal grounds under them.”

Putin’s spokesman, Dmitry Peskov, denounced them as unacceptable and said Russia’s response “will be based on the principle of reciprocity and will not take long.”