The Obama administration is prepared to take unilateral steps to sanction Russian individuals and business entities it holds responsible for corrupt and illegal behavior in Ukraine while it moves to persuade its European partners, some more reluctant than others, to consider more substantive sanctions to directly affect the Russian economy, according to senior administration officials.

The officials declined to provide a timeline but said Tuesday that Russian actions over the next few days would demonstrate whether President Vladimir Putin has any interest in an early de-escalation of the situation in the autonomous Ukrainian region of Crimea.

Even as it tried to provide Putin with a face-saving way out, the administration publicly challenged his stated reasons for deploying thousands of Russian troops across Crimea, where they have surrounded government buildings and military installations.

In statements of disbelief bordering on ridicule, President Obama and Secretary of State John F. Kerry dismissed Putin’s assertions that his troops are protecting ethnic Russians in Crimea threatened by pro-Western Ukrainians who took over the country last week in what Putin called a “coup.”

“Mr. Putin can throw a lot of words out there,” but “facts on the ground” tell a different story, Obama said following a Putin news conference in Moscow.

Kerry, during a visit to Kiev, said that Russian allegations of “ultranationalists” and “Nazis” on the streets of Ukraine were a “pretext” to further expand military occupation beyond Crimea, perhaps into Ukraine’s eastern industrial heartland.

“Not a single piece of credible evidence supports any one of these claims,” Kerry said of Putin’s charges. “None.”

Administration officials, speaking on the condition of anonymity about internal deliberations, outlined four steps that Russia could take to remove the alleged threat to its own interests and avoid sanctions.

Any danger to ethnic Russians in Ukraine could be verified and addressed by the deployment of international monitors from the United Nations or the Organization for Security and Cooperation in Europe.

Charges that Ukraine’s current U.S.-backed interim government is illegitimate, they said, could be resolved with elections in Ukraine that are currently scheduled for May.

Russia does not have to withdraw its troops from Crimea, officials said, just return them to bases it currently operates there under a long-standing agreement with Ukraine. Although Putin said Tuesday that no additional Russian troops had been sent to Crimea, administration officials have assessed that at least 6,000 were deployed late last week, in addition to about 11,000 permanently stationed there under the existing agreement.

Finally, Russia should immediately begin a dialogue with the interim government to reconfirm its long-term interest in stable relations with the neighboring state.

Obama, speaking during a visit to Powell Elementary School in the District, said there had been “some reports that President Putin is pausing for a moment and reflecting on what’s happening.”

The situation could go one of three ways, officials said.

Putin could accept what’s on offer: sending his troops back to bases, accepting international monitors and opening a dialogue with the interim government.

Russia could escalate its aggression in Ukraine, sending troops into the eastern part of the country. That possibility, while not desirable, would likely strengthen the administration’s case to European allies, led by Germany, that are reluctant to impose full-scale sanctions. Obama spoke for an hour Tuesday with German Chancellor Angela Merkel, who has indicated a desire to serve as an interlocutor with Russia.

Perhaps the most challenging scenario for the administration is the status quo, with Russian troops deployed throughout Crimea in a standoff. A similar situation has existed for years in breakaway parts of Georgia, where Russian troops have occupied northern regions of the country since 2008 while Western threats have dissipated.

Kerry plans to meet Russian Foreign Minister Sergei Lavrov this week in Europe, diplomats said.

Speaking in Kiev, Kerry announced U.S. assistance of $1 billion in loan guarantees and technical help for the placeholder government and warmly endorsed the interim leaders as statesmen. Washington will continue to support a democratic Ukraine with money and diplomatic muscle, he said, but he made no mention of a miliary show of force to counter Russia’s intervention in Crimea.

In Washington, a senior lawmaker who is expected to help steer a Ukrainian aid package through Congress, said Tuesday that the pledge of $1 billion was “welcome news.”

“The time to act is now,” House Foreign Affairs Committee Chairman Edward R. Royce (R-Calif.) said in a statement shortly after Kerry announced the aid package. “We must place crippling sanctions on Russian high-ranking officials, state-owned banks and commercial enterprises, and key individuals behind the Russian intervention. Only by forcing Putin to reverse aggression and by supporting Ukraine in this time of national crisis can we hope to restore peace in the region.”

Congress plans to debate the aid next week. It is intended in part to help protect Ukraine from likely price increases for energy if Russian supplies are slashed.

During his tour of Kiev, Kerry visited a memorial to some of the scores of civilians killed when government forces opened fire last month on street protests against the Moscow-backed government of then-President Viktor Yanukovych.

Yanukovych fled to Russia more than a week ago and maintains he is still Ukraine’s legitimate leader. Putin agreed with that Tuesday, justifying Russian intervention in Crimea as a legal response to a request from its president.

Kerry has argued that Yanukovych lost his claim to power when he fled and that the new government deserves solid Western backing to begin work and to recover stolen national assets.

Walking along muddy Institutska Street, the site of dozens of deaths from sniper and automatic weapons fire last month, Kerry passed piles of soggy flowers, many snarled in barbed wire. Remnants of barricades built of tires, packing crates, garden gates and a mattress remained.

Most of the people he spoke to appeared to be supporters of the new government.

“We are helping you,” Kerry told one woman. “President Obama wants to help you. I want to help you.”

A few moments later, a group of people who identified themselves as Russians called out to Kerry, and he also told them that the United States wants to help.

Later, Kerry met with acting President Oleksandr Turchynov, Prime Minister Arseniy Yatsenyuk and other officials who until two weeks ago were part of opposition protests calling for Yanukovych’s ouster.

Gearan reported from Kiev. Ed O’Keefe in Washington contributed to this report.