• By Kathleen Hennessey

    March 3, 2014, 1:23 p.m.

    WASHINGTON -- President Obama on Monday warned that Russia's seizure of Ukraine's Crimean peninsula will be a "costly proposition" and vowed that U.S. and Western allies will impose painful economic sanctions if Moscow does not stand down.

    "If in fact they continue on the current trajectory they're on, then we are examining a whole series of steps — economic, diplomatic — that will isolate Russia and will have a negative impact on Russia's economy and status in the world," Obama said in brief remarks in the Oval Office.

    Obama's remarks were his first public comment since Russian forces in effect seized control of Crimea, a majority Russian-speaking region of Ukraine. Obama's earlier warnings against military interference were rebuffed by Russian President Vladimir Putin, who has said Moscow must act to protect the rights of ethnic Russians from the new pro-Western government in the capital, Kiev.

    Obama administration officials said Monday that they are preparing to turn the economic screws on Moscow as they search for leverage in the standoff.

    Obama also urged Congress to pass an economic aid package that would bolster Ukraine's new government as the "first order of business" when lawmakers return to Washington. The president, who has been criticized by Republicans as being too passive in his dealings with Putin, said the speedy delivery of financial aid would send a message to Moscow.

    "I've heard a lot of talk from Congress about what should be done, what they want to do. One thing they can do right away is to work with the administration to help provide a package of assistance to the Ukrainians, to the people and that government," Obama said.

    "At this stage, there should be unanimity among Democrats and Republicans that when it comes to preserving the principle that no country has the right to send in troops to another country unprovoked, we should be able to come up with a unified position that stands outside of partisan politics."

    Obama stressed that it is not too late for Putin to change course.

    "There are really two paths that Russia can take at this point. Obviously the facts on the ground in Crimea are deeply troubling, and Russia has a large army that borders Ukraine," Obama said. "But what is also true is that over time this will be a costly proposition for Russia, and now is the time for them to consider whether they can serve their interests in a way that resorts to diplomacy as opposed to force."

    On Saturday, the White House said it was suspending preparation for a Group of 8 economic summit slated to be held in Sochi. On Monday, the White House said  the U.S. would not send a presidential delegation to the upcoming Winter Paralympic Games in Sochi.

    Obama said his interest "is seeing the Ukrainian people to be able to determine their own destiny." He acknowledged Russia's historic ties to the former Soviet republic and noted "strong commercial ties" between the two countries.

    "And so all of those interests I think can be recognized, but what cannot be done is for Russia with impunity to put its soldiers on the ground and violate basic principles that are recognized around the world. And I think the strong condemnation that has proceeded from countries around the world indicates the degree to which Russia is on the wrong side of history," he said