(Adds details about those on the sanctions list)
By Steve Holland and Jeff Mason
March 20 (Reuters) - President Barack Obama on Thursday imposed sanctions on 20 Russian citizens as well as a bank linked to Moscow's move to annex Ukraine's Crimea peninsula and threatened broader penalties against key sectors of Russia's economy if Moscow moves further into Ukraine.
Among the 20, Obama targeted several individuals close to Russian President Vladimir Putin in retaliation for his military seizure of Ukraine's Crimea region. Any assets they have in the United States will be frozen and they will also be barred from U.S. travel.
Russia's Bank Rossiya, which with $10 billion in assets is Russia's 17th largest bank, was singled out for U.S. sanctions. A Treasury Department statement said it is the personal bank for senior officials of the Russian government, including Putin's inner circle.
St. Petersburg-based Bank Rossiya is chaired and partly-owned by Yuri Kovalchuk, a close adviser to Putin. Kovalchuk, whose association with Putin dates back to the early 1990s, was among the 20 individuals targeted for sanctions.
The bank will be "frozen out of the dollar," a senior Obama administration official said.
Gennady Timchenko, one of the founders of Gunvor, which is one of the world's largest independent commodity trading companies involved in the oil and energy markets, was also singled out for penalties.
Others identified for sanctions and considered part of Putin's inner circle included Arkady Rotenberg and Boris Rotenberg, who the Treasury Department said have made "billions of dollars in contracts for Gazprom and the Sochi Winter Olympics awarded to them by Putin."
Vladimir Yakunin, chairman of the board of Russian state-owned Russian Railways, was sanctioned, as were: Andrei Fursenko, a Putin aide; Alexei Gromov, an official in the Russian presidential office; Sergei Ivanov, Putin's chief of staff, and Igor Sergun, the head of Russia's GRU military intelligence service.
The list of 20 people named on Thursday raises to 31 the number of individuals targeted for U.S. sanctions in recent days.
While individually the penalties are of limited practical impact, collectively they add up to a growing divide between the United States and Russia, in their deepest dispute since the end of the Cold War more than two decades ago.
Obama, who has already ruled out a U.S. military excursion into Ukraine, is using sanctions to try to force Russia to accept a negotiated solution, but Putin has so far resisted any serious diplomatic concessions.
In a potentially ominous move, Obama said he had signed a new executive order that clears the way for U.S. sanctions against broad sections of the Russian economy should Putin's military make moves beyond Crimea and into southern and eastern Ukraine.
Senior administration officials said many parts of the Russian economy could be targeted, including the financial services sector and the key energy, defense and mining sectors.
Russia's oil and gas industry alone accounts for nearly half of the country's annual budget revenues.
Obama, speaking at the White House, said Russia's threats to southern and eastern Ukraine posed a serious risk of escalation of the crisis in the region.
"This is not our preferred outcome. These sanctions would not only have a significant impact on the Russian economy, but could also be disruptive to the global economy. However, Russia must know that further escalation will only isolate it further from the international community," Obama said.
One official said Washington was using the new authority to prepare additional sanctions that would sting Moscow while having the smallest impact possible on the United States and its allies.
"Sanctions build over time. They are very powerful. And people may think that they are a mere wrist slap. I can assure them that they are not," the official said.
Obama also said the United States is reacting to the "dangerous risks of escalation, including threats" to Ukraine.
"These are all choices that the Russian government has made, choices that have been rejected by the international community as well as the government of Ukraine. And because of these choices the United States is today moving, as we said we would, to impose additional costs on Russia," he said.
He also promised unwavering U.S. support to NATO allies, which include Russian neighbors Lithuania, Latvia and Estonia. (Reporting by Steve Holland and Jeff Mason,; additional reporting by Susan Heavey, Lesley Wroughton, Doina Chiacu and David Storey; editing by G Crosse)