SHOWDOWN: 'There Will Be Costs' for Ukraine Military Intervention, Obama tells Russia

President Barack Obama said Thursday that “there will be costs to any military intervention in Ukraine,” after Russian military forces reportedly entered that country’s Crimea region.

“Any violation of Ukraine’s sovereignty and territorial integrity would be deeply destabilizing,” Obama said at the White House, saying the United States is “deeply concerned” about the reports of the Russian presence there.

“The Ukrainian people deserve the opportunity to determine their own future,” he said

U.S. officials confirm to NBC News that uniformed Russian forces are still entering Simferopol in Ukraine’s Crimea region. While not able to confirm the numbers used by Ukraine officials -- 2,000 or more -- the officials say they have no reason to doubt the basic information that there are Russians arriving on Russian aircraft.

Ukraine's U.N. Ambassador, Yuriy Sergeyev, told reporters Friday that "we are strong enough to defend

The Obama administration has repeatedly warned Russia not to inflame tensions in Ukraine by intervening in the volatile country.

Obama’s remarks come after deposed Ukrainian president Viktor Yanukovych pledged to “keep fighting” the new leaders of the country. Yanukovych, who has resurfaced in Russia, blamed the West for “irresponsible policies” and “pandering to” to protesters who occupied Kiev.