WASHINGTON, Jan 20 (Reuters) - Any sanctions imposed on Russia over its aggression toward Ukraine would not particularly expose the U.S. economy, although the Biden administration is focused on any possible impact on oil, the White House"s top economic official said on Thursday. "The actions that we have ready and that we are working closely with our allies to deploy would impose very significant costs across time on the Russian economy, and it would do so in a way that mitigates the impact on the global economy and the American economy," National Economic Council Director Brian Deese told CNN in an interview. "We are, as an economy, not particularly exposed to the way in which we would implement these costs. There"s obvious concern in energy markets, for example, and the risk premium in oil prices, that"s an issue that we are closely focused on and looking at how we can take actions to mitigate," he said. Western countries say they fear Russia is planning a new assault against Ukraine, nearly eight years after its forces seized the Crimea peninsula. Russia has massed tens of thousands of troops near Ukraine"s border in recent months. It denies planning an attack but says it could take unspecified military action unless a list of demands are met, including a promise from NATO never to admit Kyiv. The United States and other Western powers have raised the prospect of new sanctions targeting Moscow, possibly the severest yet, if it attacks neighboring Ukraine. read more Deese said any actions would zero in specifically on Moscow"s financials. "The reality here is the steps we are prepared to take would impose asymmetric and very significant costs on the Russian economy," he told CNN.