U.S. Senator Bob Corker, R-Tenn., ranking member of the Foreign Relations Committee, just issued a statement saying he's calling on President Obama use sanctions and other measures in leading an immediate international effort to halt Russian military intervention in Ukraine.
Corker said Russia is violating commitments made under the 1994 Budapest Memorandum and the 1997 Friendship Treaty.
"Vladimir Putin is seizing a neighboring territory — again — so President Obama must lead a meaningful, unified response with our European allies to bring an immediate halt to these provocative Russian actions, which threaten international peace and security," he said in a media release. "The Russian government has felt free to intervene militarily in Ukraine because the United States, along with Europe, has failed to make clear there would be serious, potentially irreparable consequences to such action.
"The United States and our European allies should immediately bring to bear all elements of our collective economic strength to stop Russian advances in Ukraine. Congress will consider targeted sanctions against Russian persons and entities that undermine the sovereignty and territorial integrity of Ukraine."
In a letter to President Obama on Friday, members of the Foreign Relations Committee expressed support for U.S. assistance in Ukraine and warn of Russian intervention.
Late Friday, President Barack Obama warned Russia "there will be costs" for any military maneuvers it launches in Ukraine, a move U.S. and Ukrainian officials say they believe to be already underway.
Officials say Obama may retaliate by canceling a trip to Russia this summer for an international summit and could also cut off trade discussions with Moscow. But it's unclear whether those moves will have any impact on Russia's calculus in Ukraine, which is at the center of what many see as a tug of war between East and West.
"Any violation of Ukraine's sovereignty and territorial integrity would be deeply destabilizing," Obama declared Friday in a statement from the White House. Such action by Russia would represent a "profound interference" in matters that must be decided by the Ukrainian people, he said.
Separately, Defense Secretary Chuck Hagel said that while he would not address specific U.S. options, "this could be a very dangerous situation if this continues in a provocative way." Asked about options in a CBS News interview, he said that "we're trying to deal with a diplomatic focus, that's the appropriate, responsible approach."
As Obama prepared to speak late Friday, a spokesman for the Ukrainian border service said eight Russian transport planes had landed with unknown cargo in Ukraine's Crimea region. Serhiy Astakhov told The Associated Press that the Il-76 planes arrived unexpectedly and were given permission to land, one after the other, at Gvardeiskoye air base.
U.S. officials said they also believed Russian personnel had entered Crimea. The State Department urged U.S. citizens to defer nonessential travel plans in Ukraine because of "the potential for instability."
Russian President Vladimir Putin is scheduled to host the Group of Eight economic summit in June in Sochi, the site of the recently completed Winter Olympics. The U.S. is in discussions about the summit with European partners and it is difficult to see how some of those leaders would attend the summit if Russia has forces in Crimea, according to the administration officials. They were not authorized to discuss the situation by name and spoke only on condition of anonymity.
Obama canceled a bilateral meeting with President Vladimir Putin last year after Russia granted asylum to National Security Agency leaker Edward Snowden, though Obama still attended a separate international meeting in Russia.
The administration's warning that trade talks could be halted came as Russian officials were in Washington for economic discussions with Obama advisers.
For the U.S., levying punishments on Russia is complicated by the myriad issues on which the White House needs Moscow's help. Among them: ending the bloodshed in Syria, negotiating a nuclear agreement with Iran and transporting U.S. military troops and equipment out of Afghanistan through Russian supply routes.
At the White House, a somber Obama decried the situation in Ukraine and warned about deeper outside intervention.
"Just days after the world came to Russia for the Olympic Games, that would invite the condemnation of nations around the world," he said. "The United States will stand with the international community in affirming that there will be costs for any military intervention in Ukraine."
Political turmoil in Ukraine has pushed President Viktor Yanukovych from office. Yanukovych held a news confe"ence in southern Russia Friday in which he said he was not asking Moscow for military assistance and called military action "unacceptable."
In his appearance before reporters, however, Yanukovych, who still regards himself the president, also vowed to "keep fighting for the future of Ukraine" and blamed the U.S. and the West for encouraging the rebellion that forced him to flee last weekend.