WASHINGTON--President Obama said he was "deeply concerned" on Friday over reports that Russian troops are meddling in Ukraine as armed men took up positions in Ukraine's Crimean region.
"We are now deeply concerned by reports of military movements taken by the Russian Federation inside Ukraine," Obama said in brief comments at the White House. He added, "It would be a clear violation of Russia's commitment to respect the independence and sovereignty and borders of Ukraine and of international laws."
"Any violation of Ukraine's sovereignty and territorial integrity would be deeply destabilizing, which is not in the interest of Ukraine, Russia or Europe," he said.
Earlier on Friday, Ukraine's interior ministry accused Russia of a "military invasion and occupation" saying Russian troops have taken up positions around a coast guard base and two airports on its strategic Crimea peninsula.
Ukraine's parliament also sent an urgent plea to the U.N. Security Council for a meeting on the crisis and adopted a resolution demanding Russia halt actions it says are aimed at splitting Crimea from the rest of the country.
Ukraine's autonomous province of Crimea is about 50% Russian speaking and many though not all say they identify more with Russia than Ukraine.
Russian jets this week have increased patrols along the Ukrainian border, and thousands of Russians troops have held military exercises near the Russia-Ukraine border, raising concerns about Russian interference.
Obama said that Vice President Biden spoke with Russian Prime Minister Dmitry Medvedev on Friday to express the Obama administration's concerns.
"Just days after the world came to Russia for the Olympic Games, it would invite the condemnation of nations around the world," Obama said. "And indeed the United States will stand with the international community in affirming there will be costs for any military intervention in Ukraine."
The White House on Thursday urged Russia to respect Ukraine's territorial integrity and sovereignty amid the events unfolding on the Crimea peninsula.
"We strongly support Ukraine's territorial integrity and sovereignty," Carney said. "We expect other nations to do the same. And so we are closely watching Russia's military exercises along the Ukrainian border."
Before Friday's comments, the White House has tried to downplay tensions between the U.S. and Russia over the situation in Ukraine. Obama and Russian President Vladimir Putin have also butted heads over the civil war in Syria, where the Russians have sided with Bashar Assad as the U.S. has backed the opposition.
But the Russians play an important role in international efforts to neutralize Iran's nuclear program, adding to the complications Obama faces as he deals with Putin.
Obama and Putin spoke by phone for about an hour a week ago, shortly after the Ukrainian government and opposition leaders announced a deal to head off the political crisis in Kiev.
That agreement, which was facilitated by France, Germany and Poland, but Russia did not sign on to the deal. The Russians were infuriated after Viktor Yanukovych was almost immediately deposed after the deal was cut.
Yanukovych is now in Russia, but claims that he is still Ukraine's president.